Securities Available for Sale - Disclosure on Securities Available for Sale with Temporary Impairment (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, fair value	$ 394,964	$ 89,295
12 months or longer, fair value	48,903	211,679
Total, fair value	443,867	300,974
Less than 12 months, gross unrealized losses	(2,577)	(279)
12 months or longer, gross unrealized losses	(980)	(2,951)
Total, gross unrealized losses	(3,557)	(3,230)
US Treasury Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, fair value	8,004	5,937
12 months or longer, fair value	0	0
Total, fair value	8,004	5,937
Less than 12 months, gross unrealized losses	(2)	(3)
12 months or longer, gross unrealized losses	0	0
Total, gross unrealized losses	(2)	(3)
Agency Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, fair value	59,197	24,404
12 months or longer, fair value	0	5,010
Total, fair value	59,197	29,414
Less than 12 months, gross unrealized losses	(148)	(40)
12 months or longer, gross unrealized losses	0	(23)
Total, gross unrealized losses	(148)	(63)
Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, fair value	327,263	55,488
12 months or longer, fair value	47,911	206,669
Total, fair value	375,174	262,157
Less than 12 months, gross unrealized losses	(2,427)	(221)
12 months or longer, gross unrealized losses	(970)	(2,928)
Total, gross unrealized losses	(3,397)	(3,149)
Corporate Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, fair value	500	3,466
12 months or longer, fair value	992	0
Total, fair value	1,492	3,466
Less than 12 months, gross unrealized losses	0	(15)
12 months or longer, gross unrealized losses	(10)	0
Total, gross unrealized losses	$ (10)	$ (15)