Summary of significant accounting policies - Leases (Details) |
12 Months Ended | |||
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Dec. 31, 2025
CNY (¥)
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Dec. 31, 2025
USD ($)
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Dec. 31, 2025
USD ($)
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Dec. 31, 2024
CNY (¥)
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| Lessee, Operating Lease, Liability, to be Paid, Fiscal Year Maturity [Abstract] | ||||
| 2026 | ¥ 14,761,153 | $ 2,110,817 | ||
| 2027 | 14,770,915 | 2,112,213 | ||
| 2028 | 9,250,147 | 1,322,753 | ||
| 2029 | 4,888,996 | 699,117 | ||
| 2030 | 4,888,996 | 699,117 | ||
| Thereafter | 3,911,197 | 559,294 | ||
| Total future lease payments | 52,471,404 | 7,503,311 | ||
| Less: Imputed interest | 6,807,075 | 973,398 | ||
| Total lease liability balance | ¥ 45,664,329 | $ 6,529,913 | ¥ 40,249,266 | |
| Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration] | Other Assets, Noncurrent | Other Assets, Noncurrent | Other Assets, Noncurrent | |
| Operating Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration] | Accrued Liabilities and Other Liabilities | Accrued Liabilities and Other Liabilities | Accrued Liabilities and Other Liabilities | |
| Operating Lease, Liability, Statement of Financial Position [Extensible Enumeration] | Accrued Liabilities and Other Liabilities, Other Liabilities, Noncurrent | Accrued Liabilities and Other Liabilities, Other Liabilities, Noncurrent | Accrued Liabilities and Other Liabilities, Other Liabilities, Noncurrent | |
| ROU assets | ¥ 44,778,762 | $ 6,403,278 | ¥ 39,239,747 | |
| Current lease liabilities | ¥ 10,857,421 | $ 1,552,591 | 12,732,875 | |
| Weighted average remaining lease term (in years) | 3 years 11 months 23 days | 3 years 11 months 23 days | ||
| Weighted average discount rate (as a percent) | 4.66% | 4.66% | ||
| Operating lease cost | ¥ 15,806,055 | $ 2,260,236 | ||
| Lease Cost Capitalized | 0 | ¥ 0 | ||
| Supplemental cash flow information related to operating leases | ||||
| Cash payments for operating leases | 20,271,707 | 2,898,816 | ||
| ROU assets obtained in exchange for operating lease liabilities | ¥ 10,857,421 | $ 1,552,591 | ||
| X | ||||||||||
- References No definition available.
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- Definition Amount of lessee's undiscounted obligation for lease payment for operating lease. Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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| X | ||||||||||
- Definition Amount of lessee's undiscounted obligation for lease payment for operating lease due after fifth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach). Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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| X | ||||||||||
- Definition Amount of lessee's undiscounted obligation for lease payment for operating lease to be paid in next fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach). Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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- Definition Amount of lessee's undiscounted obligation for lease payment for operating lease to be paid in fifth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach). Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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| X | ||||||||||
- Definition Amount of lessee's undiscounted obligation for lease payment for operating lease to be paid in fourth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach). Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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| X | ||||||||||
- Definition Amount of lessee's undiscounted obligation for lease payment for operating lease to be paid in third fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach). Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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| X | ||||||||||
- Definition Amount of lessee's undiscounted obligation for lease payment for operating lease to be paid in second fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach). Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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| X | ||||||||||
- Definition Amount of lessee's undiscounted obligation for lease payments in excess of discounted obligation for lease payments for operating lease. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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| X | ||||||||||
- Definition Amount of single lease cost, calculated by allocation of remaining cost of lease over remaining lease term. Includes, but is not limited to, single lease cost, after impairment of right-of-use asset, calculated by amortization of remaining right-of-use asset and accretion of lease liability. Reference 1: http://www.xbrl.org/2003/role/exampleRef
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| X | ||||||||||
- References No definition available.
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| X | ||||||||||
- Definition Present value of lessee's discounted obligation for lease payments from operating lease. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition Present value of lessee's discounted obligation for lease payments from operating lease, classified as current. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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| X | ||||||||||
- Definition Indicates line item in statement of financial position that includes current operating lease liability. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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| X | ||||||||||
- Definition Indicates line item in statement of financial position that includes operating lease liability. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition Amount of cash outflow from operating lease, excluding payments to bring another asset to condition and location necessary for its intended use. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition Amount of lessee's right to use underlying asset under operating lease. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition Indicates line item in statement of financial position that includes operating lease right-of-use asset. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition Weighted average discount rate for operating lease calculated at point in time. Reference 1: http://www.xbrl.org/2003/role/exampleRef
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- Definition Weighted average remaining lease term for operating lease, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Reference 1: http://www.xbrl.org/2003/role/exampleRef
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- Definition Amount of increase in right-of-use asset obtained in exchange for operating lease liability. Reference 1: http://www.xbrl.org/2003/role/exampleRef
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- Definition Amount of lease cost capitalized. No definition available.
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