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		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Fair Value Disclosures [Abstract]
Fair value of acquired loans at acquisition	$ 14,500,000		$ 14,500,000		$ 12,700,000
Net gains (losses) resulting from change in fair value of loans held-for-investment			(61,900)	$ (127,200)
Mortgages Held For Sale at Fair Value
Aggregate fair value	141,218,000		141,218,000		157,041,000
Aggregate unpaid principal	137,564,000		137,564,000		153,801,000
Aggregate fair value less unpaid principal	3,654,000		3,654,000		$ 3,240,000
Net gains (losses) resulting from change in fair value of loans held-for-sale	$ 250,900	$ (1,500,000)	$ 1,100,000	$ 2,400,000