Commitments and Contingencies - Summary of Allowance for Loan Repurchases or Indemnifications (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Commitments And Contingencies Disclosure [Abstract]
Balance at beginning of period	$ 3,037	$ 2,859	$ 2,659	$ 2,156
Provision for loan repurchases or indemnifications	410	470	794	1,173
Losses on loans repurchased or indemnified	(27)	13	(33)	13
Balance at end of period	$ 3,420	$ 3,342	$ 3,420	$ 3,342