Effect of Derivative Instruments on Consolidated Statements of Operations and Comprehensive Income (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Derivative Instruments, Gain (Loss) [Line Items]
(Loss) Gain Included in Mortgage Banking Income	$ (5,954)	$ (12,154)	$ (1,969)
Treasury Options
Derivative Instruments, Gain (Loss) [Line Items]
(Loss) Gain Included in Mortgage Banking Income	(262)	(2,795)	(8,222)
Eurodollar Futures
Derivative Instruments, Gain (Loss) [Line Items]
(Loss) Gain Included in Mortgage Banking Income	55	165	501
Interest Rate Swap
Derivative Instruments, Gain (Loss) [Line Items]
(Loss) Gain Included in Mortgage Banking Income	3,068	(4,561)
Forward commitments to buy/sell loans/mortgage-backed securities
Derivative Instruments, Gain (Loss) [Line Items]
(Loss) Gain Included in Mortgage Banking Income	$ (8,815)	$ (4,963)	$ 5,752