Investment Securities (Disclosure Regarding Length of Time on Securities Available for Sale with Temporary Impairment) (Detail) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, fair value	$ 42,118	$ 394,964
Less than 12 months, gross unrealized losses	(77)	(2,577)
12 months or longer, fair value	17,603	48,903
12 months or longer, gross unrealized losses	(100)	(980)
Total, fair value	59,721	443,867
Total, gross unrealized losses	(177)	(3,557)
US Treasury Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, fair value		8,004
Less than 12 months, gross unrealized losses		(2)
12 months or longer, fair value		0
12 months or longer, gross unrealized losses		0
Total, fair value		8,004
Total, gross unrealized losses	0	(2)
Agency Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, fair value	10,033	59,197
Less than 12 months, gross unrealized losses	(3)	(148)
12 months or longer, fair value	0	0
12 months or longer, gross unrealized losses	0	0
Total, fair value	10,033	59,197
Total, gross unrealized losses	(3)	(148)
Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, fair value	31,086	327,263
Less than 12 months, gross unrealized losses	(74)	(2,427)
12 months or longer, fair value	16,614	47,911
12 months or longer, gross unrealized losses	(87)	(970)
Total, fair value	47,700	375,174
Total, gross unrealized losses	(161)	(3,397)
Corporate Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, fair value	999	500
Less than 12 months, gross unrealized losses	0	0
12 months or longer, fair value	989	992
12 months or longer, gross unrealized losses	(13)	(10)
Total, fair value	1,988	1,492
Total, gross unrealized losses	$ (13)	$ (10)