Investment Securities - Disclosure Regarding Length of Time on Securities Available for Sale with Temporary Impairment (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Fair value	$ 119,143	$ 642,000
Less than 12 months, Gross unrealized losses	(297)	(19,181)
12 months or longer, Fair value	332,517	13,521
12 months or longer, Gross unrealized losses	(5,472)	(682)
Total, Fair value	451,660	655,521
Total, Gross unrealized losses	(5,769)	(19,863)
Agency Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Fair value	15,289	34,355
Less than 12 months, Gross unrealized losses	(17)	(179)
12 months or longer, Fair value	5,011	0
12 months or longer, Gross unrealized losses	(28)	0
Total, Fair value	20,300	34,355
Total, Gross unrealized losses	(45)	(179)
Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Fair value	99,820	604,778
Less than 12 months, Gross unrealized losses	(264)	(18,850)
12 months or longer, Fair value	326,848	13,521
12 months or longer, Gross unrealized losses	(5,432)	(682)
Total, Fair value	426,668	618,299
Total, Gross unrealized losses	(5,696)	(19,532)
State and Municipal Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Fair value	0	2,867
Less than 12 months, Gross unrealized losses	0	(152)
12 months or longer, Fair value	658
12 months or longer, Gross unrealized losses	(12)
Total, Fair value	658	2,867
Total, Gross unrealized losses	(12)	(152)
Corporate Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Fair value	4,034
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	4,034
Total, Gross unrealized losses	$ (16)