Investment Securities - Disclosure Regarding Length of Time on Securities Available for Sale with Temporary Impairment (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Fair value	$ 560,977	$ 642,000
Less than 12 months, Gross unrealized losses	(12,656)	(19,181)
12 months or longer, Fair value	24,780	13,521
12 months or longer, Gross unrealized losses	(609)	(682)
Total, Fair value	585,757	655,521
Total, Gross unrealized losses	(13,265)	(19,863)
Agency Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Fair value	31,196	34,355
Less than 12 months, Gross unrealized losses	(108)	(179)
12 months or longer, Fair value	0	0
12 months or longer, Gross unrealized losses	0	0
Total, Fair value	31,196	34,355
Total, Gross unrealized losses	(108)	(179)
Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Fair value	526,823	604,778
Less than 12 months, Gross unrealized losses	(12,496)	(18,850)
12 months or longer, Fair value	24,780	13,521
12 months or longer, Gross unrealized losses	(609)	(682)
Total, Fair value	551,603	618,299
Total, Gross unrealized losses	(13,105)	(19,532)
State and Municipal Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Fair value	2,958	2,867
Less than 12 months, Gross unrealized losses	(52)	(152)
12 months or longer, Fair value	0	0
12 months or longer, Gross unrealized losses	0	0
Total, Fair value	2,958	2,867
Total, Gross unrealized losses	$ (52)	$ (152)