Securities - Schedule of Amortized Cost and Fair Value of Securities Held to Maturity (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Investment Securities Held To Maturity [Line Items]
Securities Held To Maturity, Amortized Cost	$ 1,420,446	$ 1,199,169
Securities Held To Maturity, Gross Unrealized Gains	16,595	15,484
Securities Held To Maturity, Gross Unrealized Losses	(18,047)	(25,090)
Securities Held To Maturity, Fair Value	1,418,994	1,189,563
U.S. Treasury [Member]
Investment Securities Held To Maturity [Line Items]
Securities Held To Maturity, Amortized Cost	502	503
Securities Held To Maturity, Gross Unrealized Gains	123	99
Securities Held To Maturity, Gross Unrealized Losses
Securities Held To Maturity, Fair Value	625	602
U.S. Government-Sponsored Entities [Member]
Investment Securities Held To Maturity [Line Items]
Securities Held To Maturity, Amortized Cost	101,787	43,322
Securities Held To Maturity, Gross Unrealized Gains	181	180
Securities Held To Maturity, Gross Unrealized Losses	(1,284)	(1,151)
Securities Held To Maturity, Fair Value	100,684	42,351
Agency Mortgage-Backed Securities [Member]
Investment Securities Held To Maturity [Line Items]
Securities Held To Maturity, Amortized Cost	725,154	628,681
Securities Held To Maturity, Gross Unrealized Gains	12,529	12,281
Securities Held To Maturity, Gross Unrealized Losses	(3,817)	(6,032)
Securities Held To Maturity, Fair Value	733,866	634,930
Agency Collateralized Mortgage Obligations [Member]
Investment Securities Held To Maturity [Line Items]
Securities Held To Maturity, Amortized Cost	452,909	385,408
Securities Held To Maturity, Gross Unrealized Gains	1,225	764
Securities Held To Maturity, Gross Unrealized Losses	(11,976)	(15,844)
Securities Held To Maturity, Fair Value	442,158	370,328
Non-Agency Collateralized Mortgage Obligations [Member]
Investment Securities Held To Maturity [Line Items]
Securities Held To Maturity, Amortized Cost	6,352	6,852
Securities Held To Maturity, Gross Unrealized Gains	24	44
Securities Held To Maturity, Gross Unrealized Losses		(4)
Securities Held To Maturity, Fair Value	6,376	6,892
Commercial Mortgage-Backed Securities [Member]
Investment Securities Held To Maturity [Line Items]
Securities Held To Maturity, Amortized Cost	2,236	2,241
Securities Held To Maturity, Gross Unrealized Gains	121	124
Securities Held To Maturity, Gross Unrealized Losses	(15)	(37)
Securities Held To Maturity, Fair Value	2,342	2,328
States of the U.S. and Political Subdivisions [Member]
Investment Securities Held To Maturity [Line Items]
Securities Held To Maturity, Amortized Cost	131,506	132,162
Securities Held To Maturity, Gross Unrealized Gains	2,392	1,992
Securities Held To Maturity, Gross Unrealized Losses	(955)	(2,022)
Securities Held To Maturity, Fair Value	$ 132,943	$ 132,132