Securities - Schedule of Amortized Cost and Fair Value of Securities Available for Sale (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Securities Available For Sale, Amortized Cost	$ 1,139,696	$ 1,170,439
Securities Available For Sale, Gross Unrealized Gains	9,689	16,858
Securities Available For Sale, Gross Unrealized Losses	(33,827)	(14,614)
Assets measured at fair value, Available for sale securities	1,115,558	1,172,683
U.S. Government-Sponsored Entities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available For Sale, Amortized Cost	336,126	352,910
Securities Available For Sale, Gross Unrealized Gains	412	1,676
Securities Available For Sale, Gross Unrealized Losses	(4,386)	(129)
Assets measured at fair value, Available for sale securities	332,152	354,457
Agency Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available For Sale, Amortized Cost	223,125	267,575
Securities Available For Sale, Gross Unrealized Gains	4,641	7,575
Securities Available For Sale, Gross Unrealized Losses	(128)
Assets measured at fair value, Available for sale securities	227,638	275,150
Agency Collateralized Mortgage Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available For Sale, Amortized Cost	506,672	465,574
Securities Available For Sale, Gross Unrealized Gains	405	4,201
Securities Available For Sale, Gross Unrealized Losses	(18,030)	(228)
Assets measured at fair value, Available for sale securities	489,047	469,547
Non-Agency Collateralized Mortgage Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available For Sale, Amortized Cost	1,818	2,679
Securities Available For Sale, Gross Unrealized Gains	28	50
Assets measured at fair value, Available for sale securities	1,846	2,729
States of the U.S. and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available For Sale, Amortized Cost	17,472	23,592
Securities Available For Sale, Gross Unrealized Gains	542	1,232
Securities Available For Sale, Gross Unrealized Losses	(139)
Assets measured at fair value, Available for sale securities	17,875	24,824
Collateralized Debt Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available For Sale, Amortized Cost	36,451	34,765
Securities Available For Sale, Gross Unrealized Gains	2,452	967
Securities Available For Sale, Gross Unrealized Losses	(10,199)	(13,276)
Assets measured at fair value, Available for sale securities	28,704	22,456
Other Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available For Sale, Amortized Cost	16,478	21,790
Securities Available For Sale, Gross Unrealized Gains	564	695
Securities Available For Sale, Gross Unrealized Losses	(914)	(972)
Assets measured at fair value, Available for sale securities	16,128	21,513
Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available For Sale, Amortized Cost	1,138,142	1,168,885
Securities Available For Sale, Gross Unrealized Gains	9,044	16,396
Securities Available For Sale, Gross Unrealized Losses	(33,796)	(14,605)
Assets measured at fair value, Available for sale securities	1,113,390	1,170,676
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available For Sale, Amortized Cost	1,554	1,554
Securities Available For Sale, Gross Unrealized Gains	645	462
Securities Available For Sale, Gross Unrealized Losses	(31)	(9)
Assets measured at fair value, Available for sale securities	$ 2,168	$ 2,007