Securities - Schedule of Amortized Cost and Fair Value of Securities Held to Maturity (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Investment Securities Held To Maturity [Line Items]
Securities Held To Maturity, Amortized Cost	$ 1,199,169	$ 1,106,563	$ 917,212
Securities Held To Maturity, Gross Unrealized Gains	15,484	36,785	36,700
Securities Held To Maturity, Gross Unrealized Losses	(25,090)	(135)	(1,879)
Securities Held To Maturity, Fair Value	1,189,563	1,143,213	952,033
U.S. Treasury [Member]
Investment Securities Held To Maturity [Line Items]
Securities Held To Maturity, Amortized Cost	503	503	504
Securities Held To Maturity, Gross Unrealized Gains	99	188	185
Securities Held To Maturity, Gross Unrealized Losses
Securities Held To Maturity, Fair Value	602	691	689
U.S. Government-Sponsored Entities [Member]
Investment Securities Held To Maturity [Line Items]
Securities Held To Maturity, Amortized Cost	43,322	28,731	4,019
Securities Held To Maturity, Gross Unrealized Gains	180	280	175
Securities Held To Maturity, Gross Unrealized Losses	(1,151)	(99)
Securities Held To Maturity, Fair Value	42,351	28,912	4,194
Agency Mortgage-Backed Securities [Member]
Investment Securities Held To Maturity [Line Items]
Securities Held To Maturity, Amortized Cost	628,681	780,022	683,100
Securities Held To Maturity, Gross Unrealized Gains	12,281	28,783	28,722
Securities Held To Maturity, Gross Unrealized Losses	(6,032)	(1)
Securities Held To Maturity, Fair Value	634,930	808,804	711,822
Agency Collateralized Mortgage Obligations [Member]
Investment Securities Held To Maturity [Line Items]
Securities Held To Maturity, Amortized Cost	385,408	133,976	54,319
Securities Held To Maturity, Gross Unrealized Gains	764	1,266	573
Securities Held To Maturity, Gross Unrealized Losses	(15,844)		(11)
Securities Held To Maturity, Fair Value	370,328	135,242	54,881
Non-Agency Collateralized Mortgage Obligations [Member]
Investment Securities Held To Maturity [Line Items]
Securities Held To Maturity, Amortized Cost	6,852	14,082	24,348
Securities Held To Maturity, Gross Unrealized Gains	44	130	143
Securities Held To Maturity, Gross Unrealized Losses	(4)		(1,373)
Securities Held To Maturity, Fair Value	6,892	14,212	23,118
Commercial Mortgage-Backed Securities [Member]
Investment Securities Held To Maturity [Line Items]
Securities Held To Maturity, Amortized Cost	2,241	1,024
Securities Held To Maturity, Gross Unrealized Gains	124	39
Securities Held To Maturity, Gross Unrealized Losses	(37)
Securities Held To Maturity, Fair Value	2,328	1,063
States of the U.S. and Political Subdivisions [Member]
Investment Securities Held To Maturity [Line Items]
Securities Held To Maturity, Amortized Cost	132,162	147,713	147,748
Securities Held To Maturity, Gross Unrealized Gains	1,992	6,099	6,877
Securities Held To Maturity, Gross Unrealized Losses	(2,022)
Securities Held To Maturity, Fair Value	132,132	153,812	154,625
Collateralized Debt Obligations [Member]
Investment Securities Held To Maturity [Line Items]
Securities Held To Maturity, Amortized Cost		512	1,592
Securities Held To Maturity, Gross Unrealized Gains
Securities Held To Maturity, Gross Unrealized Losses		(35)	(314)
Securities Held To Maturity, Fair Value		477	1,278
Other Debt Securities [Member]
Investment Securities Held To Maturity [Line Items]
Securities Held To Maturity, Amortized Cost			1,582
Securities Held To Maturity, Gross Unrealized Gains			25
Securities Held To Maturity, Gross Unrealized Losses			(181)
Securities Held To Maturity, Fair Value			$ 1,426