Fair Value Measurements - Summary of Difference Between the Aggregate Fair Value and the Aggregate Unpaid Principal Balance for Mortgage Loans Held for Sale (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Fair Value Disclosures [Abstract]
Loans held fro investment at fair value	$ 13,300,000		$ 13,300,000		$ 12,700,000
Net gains (losses) resulting from change in fair value of loans held-for-investment			343,300	$ (65,400)
Mortgages Held For Sale at Fair Value
Aggregate fair value	140,959,000		140,959,000		157,041,000
Aggregate unpaid principal	137,524,000		137,524,000		153,801,000
Aggregate fair value less unpaid principal	3,435,000		3,435,000		$ 3,240,000
Net gains (losses) resulting from change in fair value of loans held-for-sale	$ 0	$ 2,000,000	$ 871,000	$ 3,900,000