Investment Securities (Disclosure Regarding Length of Time on Securities Available for Sale with Temporary Impairment) (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, fair value	$ 5,066	$ 226,072
Less than 12 months, gross unrealized losses	(1)	(2,282)
12 months or longer, fair value	596,594	545,880
12 months or longer, gross unrealized losses	(8,225)	(13,977)
Total, fair value	601,660	771,952
Total, gross unrealized losses	(8,226)	(16,259)
Mortgage-Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, fair value	5,066	218,175
Less than 12 months, gross unrealized losses	(1)	(2,173)
12 months or longer, fair value	591,692	545,880
12 months or longer, gross unrealized losses	(8,127)	(13,977)
Total, fair value	596,758	764,055
Total, gross unrealized losses	(8,128)	(16,150)
Corporate Obligations [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, fair value	0	7,897
Less than 12 months, gross unrealized losses	0	(109)
12 months or longer, fair value	4,902	0
12 months or longer, gross unrealized losses	(98)	0
Total, fair value	4,902	7,897
Total, gross unrealized losses	$ (98)	$ (109)