Investment Securities (Disclosure Regarding Length of Time on Securities Available for Sale with Temporary Impairment) (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Fair value	$ 293,299	$ 89,295
Less than 12 months, Gross unrealized losses	(2,357)	(279)
12 months or longer, Fair value	51,909	211,679
12 months or longer, Gross unrealized losses	(854)	(2,951)
Total, Fair value	345,208	300,974
Total, Gross unrealized losses	(3,211)	(3,230)
US Treasury Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Fair value		5,937
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		5,937
Total, Gross unrealized losses	0	(3)
Agency Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Fair value	3,053	24,404
Less than 12 months, Gross unrealized losses	(1)	(40)
12 months or longer, Fair value	0	5,010
12 months or longer, Gross unrealized losses	0	(23)
Total, Fair value	3,053	29,414
Total, Gross unrealized losses	(1)	(63)
Collateralized Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Fair value	282,309	55,488
Less than 12 months, Gross unrealized losses	(2,311)	(221)
12 months or longer, Fair value	51,909	206,669
12 months or longer, Gross unrealized losses	(854)	(2,928)
Total, Fair value	334,218	262,157
Total, Gross unrealized losses	(3,165)	(3,149)
State And Municipal Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Fair value	2,949
Less than 12 months, Gross unrealized losses	(16)
12 months or longer, Fair value	0
12 months or longer, Gross unrealized losses	0
Total, Fair value	2,949
Total, Gross unrealized losses	(16)	0
Corporate Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Fair value	4,988	3,466
Less than 12 months, Gross unrealized losses	(29)	(15)
12 months or longer, Fair value	0
12 months or longer, Gross unrealized losses	0
Total, Fair value	4,988	3,466
Total, Gross unrealized losses	$ (29)	$ (15)