Investment Securities - Investment Securities with Unrealized Losses by Aggregated Major Security Type and Length of Time in Continuous Unrealized Loss Position (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Available-for-Sale, Less than 12 Months, Fair Value	$ 390,239	$ 1,282,703
Available-for-Sale, Less than 12 Months, Unrealized Losses	(2,068)	(45,328)
Available-for-Sale, 12 months or longer, Fair Value	893,061	115,119
Available-for-Sale, 12 months or longer, Unrealized Losses	(47,883)	(20,654)
Available-for-Sale, Fair Value	1,283,300	1,397,822
Available-for-Sale, Unrealized Losses	(49,951)	(65,982)
Held-to-Maturity, Less than 12 Months, Fair Value	61,425	91,532
Held-to-Maturity, Less than 12 Months, Unrealized Losses	(650)	(1,580)
Held-to-Maturity, 12 months or longer, Fair Value	11,611
Held-to-Maturity, 12 months or longer, Unrealized Losses	(124)
Held-to-maturity, Fair Value	73,036	91,532
Held-to-Maturity, Unrealized Losses	(774)	(1,580)
U.S. Treasury [Member]
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Available-for-Sale, Less than 12 Months, Fair Value		1,900
Available-for-Sale, Less than 12 Months, Unrealized Losses
Available-for-Sale, 12 months or longer, Fair Value
Available-for-Sale, 12 months or longer, Unrealized Losses
Available-for-Sale, Fair Value		1,900
Available-for-Sale, Unrealized Losses
U.S. Government-Sponsored Entities and Agencies [Member]
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Available-for-Sale, Less than 12 Months, Fair Value	117,845	357,793
Available-for-Sale, Less than 12 Months, Unrealized Losses	(637)	(17,547)
Available-for-Sale, 12 months or longer, Fair Value	319,330	38,988
Available-for-Sale, 12 months or longer, Unrealized Losses	(11,770)	(3,452)
Available-for-Sale, Fair Value	437,175	396,781
Available-for-Sale, Unrealized Losses	(12,407)	(20,999)
Mortgage-backed Securities - Agency [Member]
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Available-for-Sale, Less than 12 Months, Fair Value	98,561	668,018
Available-for-Sale, Less than 12 Months, Unrealized Losses	(548)	(23,455)
Available-for-Sale, 12 months or longer, Fair Value	502,894	41,200
Available-for-Sale, 12 months or longer, Unrealized Losses	(20,933)	(3,112)
Available-for-Sale, Fair Value	601,455	709,218
Available-for-Sale, Unrealized Losses	(21,481)	(26,567)
Held-to-Maturity, Less than 12 Months, Fair Value		21,370
Held-to-Maturity, Less than 12 Months, Unrealized Losses		(1)
Held-to-Maturity, 12 months or longer, Fair Value
Held-to-Maturity, 12 months or longer, Unrealized Losses
Held-to-maturity, Fair Value		21,370
Held-to-Maturity, Unrealized Losses		(1)
States and Political Subdivisions [Member]
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Available-for-Sale, Less than 12 Months, Fair Value	44,466	45,077
Available-for-Sale, Less than 12 Months, Unrealized Losses	(189)	(1,620)
Available-for-Sale, 12 months or longer, Fair Value	19,794	2,812
Available-for-Sale, 12 months or longer, Unrealized Losses	(877)	(95)
Available-for-Sale, Fair Value	64,260	47,889
Available-for-Sale, Unrealized Losses	(1,066)	(1,715)
Held-to-Maturity, Less than 12 Months, Fair Value	61,425	70,162
Held-to-Maturity, Less than 12 Months, Unrealized Losses	(650)	(1,579)
Held-to-Maturity, 12 months or longer, Fair Value	11,611
Held-to-Maturity, 12 months or longer, Unrealized Losses	(124)
Held-to-maturity, Fair Value	73,036	70,162
Held-to-Maturity, Unrealized Losses	(774)	(1,579)
Pooled Trust Preferred Securities [Member]
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Available-for-Sale, Less than 12 Months, Fair Value
Available-for-Sale, Less than 12 Months, Unrealized Losses
Available-for-Sale, 12 months or longer, Fair Value	6,422	8,037
Available-for-Sale, 12 months or longer, Unrealized Losses	(11,619)	(11,178)
Available-for-Sale, Fair Value	6,422	8,037
Available-for-Sale, Unrealized Losses	(11,619)	(11,178)
Other Securities [Member]
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Available-for-Sale, Less than 12 Months, Fair Value	129,367	209,915
Available-for-Sale, Less than 12 Months, Unrealized Losses	(694)	(2,706)
Available-for-Sale, 12 months or longer, Fair Value	44,621	24,082
Available-for-Sale, 12 months or longer, Unrealized Losses	(2,684)	(2,817)
Available-for-Sale, Fair Value	173,988	233,997
Available-for-Sale, Unrealized Losses	$ (3,378)	$ (5,523)