Securities - Summaries of Fair Values and Unrealized Losses of Securities, Segregated by Length of Impairment (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014 Security	Dec. 31, 2013 Security
Schedule Of Securities [Line Items]
Number of available for sale securities, Less than 1 year	15	54
Number of available for sale securities, Greater than 1 year	29	14
Number of available for sale securities	44	68
Securities Available For Sale, Less than 12 Months, Fair Value	$ 236,060	$ 734,257
Securities Available For Sale, Less than 12 Months, Unrealized Losses	(1,263)	(26,101)
Securities Available For Sale, 12 Months or More, Fair Value	364,659	48,144
Securities Available For Sale, 12 Months or More, Unrealized Losses	(13,194)	(13,194)
Securities Available For Sale, Fair Value, Total	600,719	782,401
Securities Available For Sale, Unrealized Losses, Total	(14,457)	(39,295)
Number of held to maturity securities	60	80
Securities Held To Maturity, Less than 12 Months, Fair Value	115,779	669,220
Securities Held To Maturity, Less than 12 Months, Unrealized Losses	(403)	(24,379)
Securities Held To Maturity, Greater than 12 Months, Fair Value	365,291	15,674
Securities Held To Maturity, Greater than 12 Months, Unrealized Losses	(11,209)	(711)
Securities Held To Maturity, Fair Value, Total	481,070	684,894
Securities Held To Maturity, Unrealized Losses, Total	(11,612)	(25,090)
Less than 12 Months [Member]
Schedule Of Securities [Line Items]
Number of held to maturity securities	23	78
Greater than 12 Months [Member]
Schedule Of Securities [Line Items]
Number of held to maturity securities	37	2
U.S. Government-Sponsored Entities [Member]
Schedule Of Securities [Line Items]
Number of available for sale securities, Less than 1 year	2	17
Number of available for sale securities, Greater than 1 year	8
Number of available for sale securities	10	17
Securities Available For Sale, Less than 12 Months, Fair Value	25,647	232,962
Securities Available For Sale, Less than 12 Months, Unrealized Losses	(38)	(5,904)
Securities Available For Sale, 12 Months or More, Fair Value	113,891
Securities Available For Sale, 12 Months or More, Unrealized Losses	(2,097)
Securities Available For Sale, Fair Value, Total	139,538	232,962
Securities Available For Sale, Unrealized Losses, Total	(2,135)	(5,904)
Number of held to maturity securities	5	3
Securities Held To Maturity, Less than 12 Months, Fair Value	30,103	24,513
Securities Held To Maturity, Less than 12 Months, Unrealized Losses	(14)	(530)
Securities Held To Maturity, Greater than 12 Months, Fair Value	39,330	14,378
Securities Held To Maturity, Greater than 12 Months, Unrealized Losses	(706)	(621)
Securities Held To Maturity, Fair Value, Total	69,433	38,891
Securities Held To Maturity, Unrealized Losses, Total	(720)	(1,151)
U.S. Government-Sponsored Entities [Member] | Less than 12 Months [Member]
Schedule Of Securities [Line Items]
Number of held to maturity securities	2	2
U.S. Government-Sponsored Entities [Member] | Greater than 12 Months [Member]
Schedule Of Securities [Line Items]
Number of held to maturity securities	3	1
Agency Mortgage-Backed Securities [Member]
Schedule Of Securities [Line Items]
Number of available for sale securities, Less than 1 year	2	9
Number of available for sale securities, Greater than 1 year
Number of available for sale securities	2	9
Securities Available For Sale, Less than 12 Months, Fair Value	29,988	108,284
Securities Available For Sale, Less than 12 Months, Unrealized Losses	(28)	(1,303)
Securities Available For Sale, 12 Months or More, Fair Value
Securities Available For Sale, 12 Months or More, Unrealized Losses
Securities Available For Sale, Fair Value, Total	29,988	108,284
Securities Available For Sale, Unrealized Losses, Total	(28)	(1,303)
Number of held to maturity securities	9	25
Securities Held To Maturity, Less than 12 Months, Fair Value	13,788	308,864
Securities Held To Maturity, Less than 12 Months, Unrealized Losses	(8)	(5,942)
Securities Held To Maturity, Greater than 12 Months, Fair Value	87,376	1,296
Securities Held To Maturity, Greater than 12 Months, Unrealized Losses	(690)	(90)
Securities Held To Maturity, Fair Value, Total	101,164	310,160
Securities Held To Maturity, Unrealized Losses, Total	(698)	(6,032)
Agency Mortgage-Backed Securities [Member] | Less than 12 Months [Member]
Schedule Of Securities [Line Items]
Number of held to maturity securities	1	24
Agency Mortgage-Backed Securities [Member] | Greater than 12 Months [Member]
Schedule Of Securities [Line Items]
Number of held to maturity securities	8	1
Agency Collateralized Mortgage Obligations [Member]
Schedule Of Securities [Line Items]
Number of available for sale securities, Less than 1 year	10	26
Number of available for sale securities, Greater than 1 year	16	2
Number of available for sale securities	26	28
Securities Available For Sale, Less than 12 Months, Fair Value	178,355	389,989
Securities Available For Sale, Less than 12 Months, Unrealized Losses	(1,187)	(18,644)
Securities Available For Sale, 12 Months or More, Fair Value	243,377	34,229
Securities Available For Sale, 12 Months or More, Unrealized Losses	(10,413)	(2,150)
Securities Available For Sale, Fair Value, Total	421,732	424,218
Securities Available For Sale, Unrealized Losses, Total	(11,600)	(20,794)
Number of held to maturity securities	20	21
Securities Held To Maturity, Less than 12 Months, Fair Value	50,237	301,312
Securities Held To Maturity, Less than 12 Months, Unrealized Losses	(281)	(15,844)
Securities Held To Maturity, Greater than 12 Months, Fair Value	224,392
Securities Held To Maturity, Greater than 12 Months, Unrealized Losses	(9,497)
Securities Held To Maturity, Fair Value, Total	274,629	301,312
Securities Held To Maturity, Unrealized Losses, Total	(9,778)	(15,844)
Agency Collateralized Mortgage Obligations [Member] | Less than 12 Months [Member]
Schedule Of Securities [Line Items]
Number of held to maturity securities	4	21
Agency Collateralized Mortgage Obligations [Member] | Greater than 12 Months [Member]
Schedule Of Securities [Line Items]
Number of held to maturity securities	16
Commercial Mortgage-Backed Securities [Member]
Schedule Of Securities [Line Items]
Number of held to maturity securities		1
Securities Held To Maturity, Less than 12 Months, Fair Value		984
Securities Held To Maturity, Less than 12 Months, Unrealized Losses		(37)
Securities Held To Maturity, Greater than 12 Months, Fair Value
Securities Held To Maturity, Greater than 12 Months, Unrealized Losses
Securities Held To Maturity, Fair Value, Total		984
Securities Held To Maturity, Unrealized Losses, Total		(37)
Commercial Mortgage-Backed Securities [Member] | Less than 12 Months [Member]
Schedule Of Securities [Line Items]
Number of held to maturity securities		1
Commercial Mortgage-Backed Securities [Member] | Greater than 12 Months [Member]
Schedule Of Securities [Line Items]
Number of held to maturity securities
States of the U.S. and Political Subdivisions [Member]
Schedule Of Securities [Line Items]
Number of available for sale securities, Less than 1 year	1	2
Number of available for sale securities, Greater than 1 year	1
Number of available for sale securities	2	2
Securities Available For Sale, Less than 12 Months, Fair Value	2,070	3,022
Securities Available For Sale, Less than 12 Months, Unrealized Losses	(10)	(250)
Securities Available For Sale, 12 Months or More, Fair Value	1,128
Securities Available For Sale, 12 Months or More, Unrealized Losses	(64)
Securities Available For Sale, Fair Value, Total	3,198	3,022
Securities Available For Sale, Unrealized Losses, Total	(74)	(250)
Number of held to maturity securities	23	27
Securities Held To Maturity, Less than 12 Months, Fair Value	18,846	31,537
Securities Held To Maturity, Less than 12 Months, Unrealized Losses	(93)	(2,022)
Securities Held To Maturity, Greater than 12 Months, Fair Value	14,193
Securities Held To Maturity, Greater than 12 Months, Unrealized Losses	(316)
Securities Held To Maturity, Fair Value, Total	33,039	31,537
Securities Held To Maturity, Unrealized Losses, Total	(409)	(2,022)
States of the U.S. and Political Subdivisions [Member] | Less than 12 Months [Member]
Schedule Of Securities [Line Items]
Number of held to maturity securities	13	27
States of the U.S. and Political Subdivisions [Member] | Greater than 12 Months [Member]
Schedule Of Securities [Line Items]
Number of held to maturity securities	10
Other Securities [Member]
Schedule Of Securities [Line Items]
Number of available for sale securities, Less than 1 year
Number of available for sale securities, Greater than 1 year	4	4
Number of available for sale securities	4	4
Securities Available For Sale, Less than 12 Months, Fair Value
Securities Available For Sale, Less than 12 Months, Unrealized Losses
Securities Available For Sale, 12 Months or More, Fair Value	6,263	5,950
Securities Available For Sale, 12 Months or More, Unrealized Losses	(620)	(929)
Securities Available For Sale, Fair Value, Total	6,263	5,950
Securities Available For Sale, Unrealized Losses, Total	(620)	(929)
Collateralized Debt Obligations [Member]
Schedule Of Securities [Line Items]
Number of available for sale securities, Less than 1 year
Number of available for sale securities, Greater than 1 year		8
Number of available for sale securities		8
Securities Available For Sale, Less than 12 Months, Fair Value
Securities Available For Sale, Less than 12 Months, Unrealized Losses
Securities Available For Sale, 12 Months or More, Fair Value		7,965
Securities Available For Sale, 12 Months or More, Unrealized Losses		(10,115)
Securities Available For Sale, Fair Value, Total		7,965
Securities Available For Sale, Unrealized Losses, Total		(10,115)
Non-Agency Collateralized Mortgage Obligations [Member]
Schedule Of Securities [Line Items]
Number of held to maturity securities	3	3
Securities Held To Maturity, Less than 12 Months, Fair Value	2,805	2,010
Securities Held To Maturity, Less than 12 Months, Unrealized Losses	(7)	(4)
Securities Held To Maturity, Greater than 12 Months, Fair Value
Securities Held To Maturity, Greater than 12 Months, Unrealized Losses
Securities Held To Maturity, Fair Value, Total	2,805	2,010
Securities Held To Maturity, Unrealized Losses, Total	$ (7)	$ (4)
Non-Agency Collateralized Mortgage Obligations [Member] | Less than 12 Months [Member]
Schedule Of Securities [Line Items]
Number of held to maturity securities	3	3
Non-Agency Collateralized Mortgage Obligations [Member] | Greater than 12 Months [Member]
Schedule Of Securities [Line Items]
Number of held to maturity securities