Investment Securities - Securities Available for Sale (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	$ 1,128,221	$ 1,162,332
Gross unrealized gains	15,185	15,125
Gross unrealized losses	(13,265)	(19,863)
Fair value	1,130,141	1,157,594
Agency Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	93,064	93,223
Gross unrealized gains	335	372
Gross unrealized losses	(108)	(179)
Fair value	93,291	93,416
Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	1,027,193	1,060,013
Gross unrealized gains	14,599	14,493
Gross unrealized losses	(13,105)	(19,532)
Fair value	1,028,687	1,054,974
State and Municipal Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	7,567	8,739
Gross unrealized gains	154	171
Gross unrealized losses	(52)	(152)
Fair value	7,669	8,758
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	397	357
Gross unrealized gains	97	89
Gross unrealized losses	0	0
Fair value	$ 494	$ 446