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Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Thousands | 3 Months Ended | 12 Months Ended
--- | --- | ---
Sep. 30, 2015 | Dec. 31, 2015 | Dec. 31, 2014 | Dec. 31, 2013
Significant Accounting Policies [Line Items] |  |  |  |
Risk-sharing arrangement term |  | 10 years |  |
Special Purpose Entities, assets |  | $ 63,000 | $ 19,000 |
Special Purpose Entities, liabilities |  | $ 25,000 | 7,000 |
Incentive Plan, awards vesting period |  | 3 years |  |
Incentive Plan, mandatory holding period before awards vest |  | 3 years |  |
Employee Stock Purchase Plan, percentage of common stock fair value that employees can purchase |  | 85.00% |  |
Employees maximum 401(k) contribution |  | 100.00% |  |
Employer matching contributions |  | $ 800 | 600 | $ 200
Minimum |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |
Percentage of losses assumed on pool of loans sold | 1.00% |  |  |
Incentive Plan, awards vesting period |  | 3 years |  |
Maximum |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |
Percentage of losses assumed on pool of loans sold | 2.25% |  |  |
Incentive Plan, awards vesting period |  | 4 years |  |
Accounting Standards Update 2014-13 |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |
Cumulative effect adjustment - adoption of ASU 2014-13 |  |  | 9,728 |
Accounting Standards Update 2014-13 | Cumulative Earnings |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |
Cumulative effect adjustment - adoption of ASU 2014-13 |  |  | $ 9,728 |

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