Securities - Schedule of Unrealized Loss and Fair Value on Investments (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Total temporarily impaired securities, Less than 12 months, Fair Value	$ 458,059	$ 234,315
Total temporarily impaired securities, Less than 12 months, Unrealized Losses	(14,212)	(1,811)
Total temporarily impaired securities,12 months or longer, Fair Value	52,035	13,939
Total temporarily impaired securities, 12 months or longer, Unrealized Losses	(781)	(185)
Total temporarily impaired securities, Fair Value	510,094	248,254
Total temporarily impaired securities, Unrealized Losses	(14,993)	(1,996)
Mortgage-Backed Securities of U.S. Government Sponsored Entities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Fair Value	67,243	54,289
Less than 12 months, Unrealized Losses	(3,451)	(469)
12 months or longer, Fair Value	14,719	0
12 months or longer, Unrealized Losses	(225)	0
Fair Value, Total	81,962	54,289
Unrealized Losses, Total	(3,676)	(469)
Collateralized Mortgage Obligations of U.S. Government Sponsored Entities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Fair Value	291,428	150,057
Less than 12 months, Unrealized Losses	(9,590)	(901)
12 months or longer, Fair Value	37,191	4,593
12 months or longer, Unrealized Losses	(554)	(93)
Fair Value, Total	328,619	154,650
Unrealized Losses, Total	(10,144)	(994)
Privately Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Fair Value	29,112
Less than 12 months, Unrealized Losses	(642)
12 months or longer, Fair Value	0
12 months or longer, Unrealized Losses	0
Fair Value, Total	29,112
Unrealized Losses, Total	(642)
Private Collateralized Mortgage Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Fair Value	42,432	29,969
Less than 12 months, Unrealized Losses	(297)	(441)
12 months or longer, Fair Value	0	9,221
12 months or longer, Unrealized Losses	0	(89)
Fair Value, Total	42,432	39,190
Unrealized Losses, Total	(297)	(530)
Collateralized Loan Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Fair Value	27,334
Less than 12 months, Unrealized Losses	(226)
12 months or longer, Fair Value	0
12 months or longer, Unrealized Losses	0
Fair Value, Total	27,334
Unrealized Losses, Total	(226)
Obligations of State and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Fair Value	510	0
Less than 12 months, Unrealized Losses	(6)	0
12 months or longer, Fair Value	125	125
12 months or longer, Unrealized Losses	(2)	(3)
Fair Value, Total	635	125
Unrealized Losses, Total	$ (8)	$ (3)