Commitments and Contingencies - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Commitments And Contingencies Disclosure [Abstract]
Total principal amount of loans repurchased or indemnified	$ 1,543	$ 921	$ 2,662	$ 1,770