Fair Value - Schedule of Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale debt securities	$ 1,458,120	$ 2,048,442
Derivative assets	16,062	20,093
Total recurring fair value measurements - assets	1,474,182	2,068,535
Derivative liabilities	15,929	21,100
Total recurring fair value measurements - liabilities	15,929	21,100
U.S. Treasury and government agency securities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale debt securities	620	18,265
Municipal obligations [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale debt securities	43,648	50,165
Corporate debt securities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale debt securities	3,500	2,250
Mortgage-backed securities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale debt securities	1,359,970	1,774,406
Collateralized mortgage obligations [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale debt securities	45,032	198,077
Equity securities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale debt securities	5,350	5,279
Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale debt securities	9,470	25,794
Total recurring fair value measurements - assets	9,470	25,794
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	620	18,265
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	2,250
Level 1 [Member] | Equity securities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale debt securities	5,350	5,279
Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale debt securities	1,448,650	2,022,648
Derivative assets	16,062	20,093
Total recurring fair value measurements - assets	1,464,712	2,042,741
Derivative liabilities	15,929	21,100
Total recurring fair value measurements - liabilities	15,929	21,100
Level 2 [Member] | Municipal obligations [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale debt securities	43,648	50,165
Level 2 [Member] | Mortgage-backed securities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale debt securities	1,359,970	1,774,406
Level 2 [Member] | Collateralized mortgage obligations [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available for sale debt securities	$ 45,032	$ 198,077