Fair Value - Schedule of Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale debt securities	$ 1,333,401	$ 1,421,772
Derivative assets	17,700	15,579
Total recurring fair value measurements-assets	1,351,101	1,437,351
Derivative liabilities	18,458	15,006
Total recurring fair value measurements-liabilities	18,458	15,006
Municipal obligations [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale debt securities	20,837	35,961
U.S. Treasury and government agency securities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale debt securities	282	505
Corporate debt securities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale debt securities	3,500	3,500
Mortgage-backed securities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale debt securities	1,208,125	1,276,958
Collateralized mortgage obligations [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale debt securities	90,948	94,125
Equity securities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale debt securities	9,709	10,723
Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale debt securities	13,491	14,728
Derivative assets
Total recurring fair value measurements-assets	13,491	14,728
Derivative liabilities
Total recurring fair value measurements-liabilities
Level 1 [Member] | Municipal obligations [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale debt securities
Level 1 [Member] | U.S. Treasury and government agency securities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale debt securities	282	505
Level 1 [Member] | Corporate debt securities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale debt securities	3,500	3,500
Level 1 [Member] | Mortgage-backed securities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale debt securities
Level 1 [Member] | Collateralized mortgage obligations [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale debt securities
Level 1 [Member] | Equity securities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale debt securities	9,709	10,723
Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale debt securities	1,319,910	1,407,044
Derivative assets	17,700	15,579
Total recurring fair value measurements-assets	1,337,610	1,422,623
Derivative liabilities	18,458	15,006
Total recurring fair value measurements-liabilities	18,458	15,006
Level 2 [Member] | Municipal obligations [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale debt securities	20,837	35,961
Level 2 [Member] | U.S. Treasury and government agency securities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale debt securities
Level 2 [Member] | Corporate debt securities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale debt securities
Level 2 [Member] | Mortgage-backed securities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale debt securities	1,208,125	1,276,958
Level 2 [Member] | Collateralized mortgage obligations [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale debt securities	90,948	94,125
Level 2 [Member] | Equity securities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale debt securities