Effect of Derivative Instruments on Consolidated Statements of Income and Comprehensive Income (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Included in Mortgage Banking Income	$ (4,128)	$ (6,211)	$ (8,284)	$ 6,056
Treasury Options
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Included in Mortgage Banking Income	(1,147)	(6,245)	(4,397)	3,619
Eurodollar Futures
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Included in Mortgage Banking Income	(90)	17	(163)	(38)
Interest Rate Swap
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Included in Mortgage Banking Income	(2,449)	(1,751)	(202)	2,427
Forward commitments to buy/sell loans/mortgage-backed securities
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Included in Mortgage Banking Income	$ (442)	$ 1,768	$ (3,522)	$ 48