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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Additional Information (Detail) | 12 Months Ended |  |
--- | --- | --- | ---
Dec. 31, 2020 CNY (¥) | Dec. 31, 2020 USD ($) | Dec. 31, 2019 CNY (¥) | Dec. 31, 2018 CNY (¥) | Dec. 31, 2020 USD ($) | Jan. 01, 2019 USD ($)
Working capital | ¥ (46,899,000) |  |  |  |  |
Net cash used in the operating activities | (35,505,000) | $ (5,439,000) | ¥ 26,291,000 | ¥ (228,368,000) |  |
Net income | 250,066,000 | $ 38,325,000 | 527,185,000 | 611,758,000 |  |
Shareholders' deficit | (461,623,000) |  | (741,854,000) |  | $ (70,747,000) |
Cash and cash equivalents | ¥ 117,320,000 |  | ¥ 122,149,000 | ¥ 41,441,000 | $ 17,980,000 |
VIEs percentage of Group's consolidated revenue | 48.00% | 48.00% | 96.00% | 100.00% |  |
VIEs percentage of consolidated total assets | 12.00% | 12.00% | 52.00% |  |  |
VIEs percentage of consolidated total liabilities | 86.00% | 86.00% | 95.00% |  |  |
Convenience translation rate per US$1.00 | 6.5250 |  |  |  | 6.5250 |
Value added tax rate | 6.00% | 6.00% |  |  |  |
Value added tax amount | ¥ 92,161,000 |  | ¥ 168,763,000 | ¥ 298,720,000 |  |
Deferred Revenue |  |  | 55,689,000 |  |  |
Service fees | 23,815,000 |  | 174,191,000 | 242,513,000 |  |
Refund liabilities | (180,104,000) | $ (27,602,000) | 15,505,000 | (71,613,000) |  |
Employee defined contribution plan expense | 37,665,000 |  | 65,076,000 | 51,611,000 |  |
Advertising expense | 21,697,000 |  | 26,985,000 | 25,994,000 |  |
Government grants | ¥ 6,773,000 |  | ¥ 18,722,000 | 22,465,000 |  |
Weighted average remaining lease term | 1 year 8 months 12 days |  | 1 year 2 months 12 days |  | 1 year 8 months 12 days |
Weighted average discount rate | 4.75% |  | 4.75% |  | 4.75% |
Retained earnings | ¥ (1,266,848,000) |  | ¥ (1,519,731,000) |  | $ (194,153,000) |
Cumulative Effect Adjustment | ASU 2016-02 |  |  |  |  |  |
Retained earnings | $ |  |  |  |  |  | $ 0
Other Revenue [Member] |  |  |  |  |  |
Refund liabilities | 77,045,000 |  |  |  |  |
Accrued Expenses and Other Current Liabilities |  |  |  |  |  |
Deferred Revenue | 4,154,000 |  |  |  |  |
Post-origination service |  |  |  |  |  |
Remaining performance obligations |  |  | ¥ 182,026,000 | ¥ 222,735,000 |  |
Remaining performance obligations, percentage that will be recognized by the Group over the following 12 months |  |  | 100.00% | 92.00% |  |
CNY |  |  |  |  |  |
Cash and cash equivalents | ¥ 63,197,000 |  | ¥ 78,296,000 |  |  |
Cash and Cash Equivalents | Net Assets, Geographic Area | CHINA |  |  |  |  |  |
Concentration risk, percentage | 53.00% | 53.00% | 64.00% |  |  |
Customer Concentration Risk | Net Revenue | Customer A |  |  |  |  |  |
Concentration risk, percentage | 17.00% | 17.00% |  |  |  |
Customer Concentration Risk | Net Revenue | Customer B |  |  |  |  |  |
Concentration risk, percentage | 13.00% | 13.00% |  |  |  |
Customer Concentration Risk | Accounts Receivable and Contract Assets | Customer A |  |  |  |  |  |
Concentration risk, percentage | 14.00% | 14.00% |  |  |  |
Customer Concentration Risk | Accounts Receivable and Contract Assets | Customer C |  |  |  |  |  |
Concentration risk, percentage | 24.00% | 24.00% |  |  |  |
Equity Pledge Agreement |  |  |  |  |  |
Percentage of equity interest in Jiayin Finance pledged to WFOE | 100.00% | 100.00% |  |  |  |
Exclusive Purchase Agreement Member [Member] | Shanghai Kunjia Technology Co., Ltd. ("Shanghai Kunjia" or "WFOE") [Member] |  |  |  |  |  |
Consideration of purchase | ¥ 1 |  |  |  |  |
Effective time period of agreement | 10 years | 10 years |  |  |  |
Payment Guarantee [Member] |  |  |  |  |  |
Guarantee obligations | ¥ 1,586,610,000 |  | ¥ 487,216,000 |  |  |

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