Fair Value Measurements - Amount of Net Gains (Losses) from Fair Value Changes (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Fair Value Disclosures [Abstract]
Mortgage loans held for sale, at fair value	$ 100	$ (1,041)	$ 3,631	$ (2,513)
Mortgage loans held for investment, at fair value	$ (14)	$ (296)	$ 73	$ (1,217)