Investment Securities - Investment Securities in Continuous Unrealized Loss Position (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Estimated fair value, Less than 12 months	$ 1,760,369	$ 1,699,426
Available For Sale Securities Continuous Unrealized Losses Position Less Than Twelve Months Aggregate Losses	(7,419)	(19,458)
Estimated fair value, 12 months or more	117,260	116,330
Available For Sale Securities Continuous Unrealized Loss Position Twelve Months Or More Aggregate Losses	(18,242)	(20,454)
Held to maturity, Estimated fair value, Less than 12 months	1,732,639	2,643,467
Held To Maturity Securities Continuous Unrealized Loss Position Less Than12 Months Aggregate Losses	(37,873)	(65,269)
Held to maturity, Estimated fair value, 12 months or more	166,873	160,563
Held To Maturity Securities Continuous Unrealized Loss Position12 Months Or Longer Aggregate Losses	(51,473)	(60,638)
Total investment securities, fair value less than 12 months	3,493,008	4,342,893
Investment Securities Continuous Unrealized Loss Position Less Than Twelve Months Aggregate Losses	(45,292)	(84,727)
Total of investment securities, fair value, 12 Months or More	284,133	276,893
Investment Securities Continuous Unrealized Loss Position Twelve Months or Longer Aggregate Losses	(69,715)	(81,092)
Government Issued or Guaranteed [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Estimated fair value, Less than 12 months	1,725,859	1,697,094
Available For Sale Securities Continuous Unrealized Losses Position Less Than Twelve Months Aggregate Losses	(6,919)	(19,225)
Estimated fair value, 12 months or more	5,215	5,815
Available For Sale Securities Continuous Unrealized Loss Position Twelve Months Or More Aggregate Losses	(131)	(125)
Held to maturity, Estimated fair value, Less than 12 months	1,715,149	2,629,950
Held To Maturity Securities Continuous Unrealized Loss Position Less Than12 Months Aggregate Losses	(37,718)	(65,149)
Held to maturity, Estimated fair value, 12 months or more
Held To Maturity Securities Continuous Unrealized Loss Position12 Months Or Longer Aggregate Losses
Privately Issued Mortgage-Backed Securities [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Held to maturity, Estimated fair value, Less than 12 months
Held To Maturity Securities Continuous Unrealized Loss Position Less Than12 Months Aggregate Losses
Held to maturity, Estimated fair value, 12 months or more	164,215	159,005
Held To Maturity Securities Continuous Unrealized Loss Position12 Months Or Longer Aggregate Losses	(51,434)	(60,623)
Privately Issued Mortgage-Backed Securities [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Estimated fair value, Less than 12 months
Available For Sale Securities Continuous Unrealized Losses Position Less Than Twelve Months Aggregate Losses
Estimated fair value, 12 months or more	91	98
Available For Sale Securities Continuous Unrealized Loss Position Twelve Months Or More Aggregate Losses	(5)	(5)
Obligations of States and Political Subdivisions [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Estimated fair value, Less than 12 months	1,930
Available For Sale Securities Continuous Unrealized Losses Position Less Than Twelve Months Aggregate Losses	(68)
Estimated fair value, 12 months or more	439	558
Available For Sale Securities Continuous Unrealized Loss Position Twelve Months Or More Aggregate Losses	(3)	(6)
Held to maturity, Estimated fair value, Less than 12 months	17,490	13,517
Held To Maturity Securities Continuous Unrealized Loss Position Less Than12 Months Aggregate Losses	(155)	(120)
Held to maturity, Estimated fair value, 12 months or more	2,658	1,558
Held To Maturity Securities Continuous Unrealized Loss Position12 Months Or Longer Aggregate Losses	(39)	(15)
U.S. Treasury and federal agencies [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Estimated fair value, Less than 12 months	29,346	745
Available For Sale Securities Continuous Unrealized Losses Position Less Than Twelve Months Aggregate Losses	(59)	(2)
Estimated fair value, 12 months or more
Available For Sale Securities Continuous Unrealized Loss Position Twelve Months Or More Aggregate Losses
Collateralized Debt Obligations [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Estimated fair value, Less than 12 months
Available For Sale Securities Continuous Unrealized Losses Position Less Than Twelve Months Aggregate Losses
Estimated fair value, 12 months or more	6,097	6,257
Available For Sale Securities Continuous Unrealized Loss Position Twelve Months Or More Aggregate Losses	(306)	(857)
Other Debt Securities [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Estimated fair value, Less than 12 months	927	1,428
Available For Sale Securities Continuous Unrealized Losses Position Less Than Twelve Months Aggregate Losses	(10)	(4)
Estimated fair value, 12 months or more	105,418	103,602
Available For Sale Securities Continuous Unrealized Loss Position Twelve Months Or More Aggregate Losses	(17,797)	(19,461)
Equity Securities [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Estimated fair value, Less than 12 months	2,307	159
Available For Sale Securities Continuous Unrealized Losses Position Less Than Twelve Months Aggregate Losses	(363)	(227)
Estimated fair value, 12 months or more
Available For Sale Securities Continuous Unrealized Loss Position Twelve Months Or More Aggregate Losses