Securities Available for Sale - Schedule of Securities Available for Sale Portfolio (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	$ 1,065,482	$ 1,051,311
Unrealized gains	37,834	30,234
Unrealized losses	(9,962)	(18,529)
Fair value	1,093,354	1,063,016
Trust Preferred Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	45,399	45,589
Unrealized gains	331	225
Unrealized losses	(6,876)	(6,908)
Fair value	38,854	38,906
Municipal Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	172,249	178,579
Unrealized gains	8,746	5,310
Unrealized losses	(683)	(4,149)
Fair value	180,312	179,740
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	677	953
Unrealized gains	776	968
Unrealized losses
Fair value	1,453	1,921
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	181,854	201,268
Unrealized gains	4,764	5,313
Unrealized losses		(361)
Fair value	186,618	206,220
U.S. Sponsored Entities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	663,756	623,134
Unrealized gains	23,192	18,397
Unrealized losses	(2,403)	(7,107)
Fair value	684,545	634,424
Private Label [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	1,547	1,788
Unrealized gains	25	21
Unrealized losses		(4)
Fair value	1,572	1,805
Subtotal Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	665,303	624,922
Unrealized gains	23,217	18,418
Unrealized losses	(2,403)	(7,111)
Fair value	$ 686,117	$ 636,229