Accumulated change in equity from transactions and other events and circumstances from non-owner sources, net of tax effect, at period end. Excludes Net Income (Loss), and accumulated changes in equity from transactions resulting from investments by owners and distributions to owners. Includes foreign currency translation items, certain pension adjustments, unrealized gains and losses on certain investments in debt and equity securities, other than temporary impairment (OTTI) losses related to factors other than credit losses on available-for-sale and held-to-maturity debt securities that an entity does not intend to sell and it is not more likely than not that the entity will be required to sell before recovery of the amortized cost basis, as well as changes in the fair value of derivatives related to the effective portion of a designated cash flow hedge.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=118930883&loc=d3e637-108580

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 14A
-URI http://asc.fasb.org/extlink&oid=118930883&loc=SL7669686-108580

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 14
-URI http://asc.fasb.org/extlink&oid=118930883&loc=d3e681-108580

Summary of significant accounting policies (Details)	12 Months Ended
Summary of significant accounting policies (Details)	Dec. 31, 2019 USD ($)	Dec. 31, 2019 CNY (¥)	Dec. 31, 2019 CNY (¥)	Jan. 01, 2019 USD ($)	Jan. 01, 2019 CNY (¥)	Dec. 31, 2018 CNY (¥)
Lessee, Lease, Description [Line Items]
Right-of-use assets, net	$ 8,943,835		¥ 62,265,193
Lessee, Operating Lease, Liability, Payment, Due [Abstract]
2020	3,641,507		25,351,439
2021	3,561,452		24,794,120
2022	2,721,413		18,945,931
Total future lease payments	9,924,372		69,091,490
Less: Imputed interest	944,920		6,578,343
Total lease liability balance	8,979,452		¥ 62,513,147
Total cash outflows for leases	$ 3,078,578	¥ 21,432,442
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	Other Assets, Noncurrent		Other Assets, Noncurrent
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	Other Assets, Noncurrent		Other Assets, Noncurrent
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	Other Liabilities, Noncurrent		Other Liabilities, Noncurrent
ROU assets	$ 8,943,835		¥ 62,265,193
Current lease liabilities	$ 2,903,426		¥ 20,213,070
Weighted average remaining lease term (in years)	1 year 11 months 1 day		1 year 11 months 1 day
Weighted average discount rate (as a percent)	6.20%		6.20%
Operating lease cost	$ 3,254,909	22,660,022
Other comprehensive income	9,638,427		¥ 67,100,802			¥ 52,494,757
Supplemental cash flow information related to operating leases
ROU assets obtained in exchange for operating lease liabilities	4,590,511	¥ 31,958,216
ASU 2016-02 Leases (Topic 842) \| Restatement adjustment
Lessee, Lease, Description [Line Items]
Right-of-use assets, net				$ 9,365,940	¥ 65,203,798
Lessee, Operating Lease, Liability, Payment, Due [Abstract]
Total lease liability balance				9,365,940	65,203,798
ROU assets				$ 9,365,940	¥ 65,203,798
Current lease liabilities	2,903,448		20,213,223
ASU 2016-13 Financial Instruments-Credit Losses (Topic 326) \| Restatement adjustment
Lessee, Operating Lease, Liability, Payment, Due [Abstract]
Other comprehensive income	$ 2,480,000		¥ 17,240,000