Securities Available for Sale - Schedule of Securities Available for Sale Portfolio (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	$ 1,049,130	$ 1,065,447
Unrealized gains	34,659	55,144
Unrealized losses	(16,388)	(9,815)
Fair value	1,067,401	1,110,776
Trust Preferred Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	45,898	45,894
Unrealized gains	245	367
Unrealized losses	(7,655)	(8,234)
Fair value	38,488	38,027
Municipal Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	176,076	177,414
Unrealized gains	6,649	13,717
Unrealized losses	(3,288)	(244)
Fair value	179,437	190,887
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	953	1,142
Unrealized gains	776	676
Unrealized losses
Fair value	1,729	1,818
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	209,153	219,700
Unrealized gains	6,044	7,186
Unrealized losses	(477)	(1,091)
Fair value	214,720	225,795
U.S. Sponsored Entities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	615,116	617,158
Unrealized gains	20,921	33,021
Unrealized losses	(4,966)	(246)
Fair value	631,071	649,933
Private Label [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	1,934	4,139
Unrealized gains	24	177
Unrealized losses	(2)
Fair value	1,956	4,316
Subtotal Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	617,050	621,297
Unrealized gains	20,945	33,198
Unrealized losses	(4,968)	(246)
Fair value	$ 633,027	$ 654,249