Investment Securities (Disclosure Regarding Length of Time on Securities Available for Sale with Temporary Impairment) (Detail) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, fair value	$ 570,958	$ 568,290
Less than 12 months, gross unrealized losses	(7,119)	(8,405)
12 months or longer, fair value	1,055	1,055
12 months or longer, gross unrealized losses	(14)	(14)
Total, fair value	572,013	569,345
Total, gross unrealized losses	(7,133)	(8,419)
Agency Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, fair value	23,046	14,000
Less than 12 months, gross unrealized losses	(27)	(25)
12 months or longer, fair value	0	0
12 months or longer, gross unrealized losses	0	0
Total, fair value	23,046	14,000
Total, gross unrealized losses	(27)	(25)
Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, fair value	547,912	553,629
Less than 12 months, gross unrealized losses	(7,092)	(8,377)
12 months or longer, fair value	65	65
12 months or longer, gross unrealized losses	(3)	(3)
Total, fair value	547,977	553,694
Total, gross unrealized losses	(7,095)	(8,380)
State And Municipal Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, fair value		661
Less than 12 months, gross unrealized losses		(3)
12 months or longer, fair value		0
12 months or longer, gross unrealized losses		0
Total, fair value		661
Total, gross unrealized losses	0	(3)
Corporate Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, fair value	0	0
Less than 12 months, gross unrealized losses	0	0
12 months or longer, fair value	990	990
12 months or longer, gross unrealized losses	(11)	(11)
Total, fair value	990	990
Total, gross unrealized losses	$ (11)	$ (11)