Fair Value Measurements - Financial Assets and Financial Liabilities Measured at Fair Value on a Recurring Basis (Details) (Fair Value Measured on a Recurring Basis, USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Estimated Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Mortgage servicing rights	$ 25,698	$ 16,373
Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Mortgage servicing rights	0	0
Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Mortgage servicing rights	25,698	16,373
Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Mortgage servicing rights	0	0
Obligations of U.S. government agencies | Estimated Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Investment securities available-for-sale	763,238	754,856
Obligations of U.S. government agencies | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Investment securities available-for-sale	0	0
Obligations of U.S. government agencies | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Investment securities available-for-sale	763,238	754,856
Obligations of U.S. government agencies | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Investment securities available-for-sale	0	0
U.S. agency residential mortgage-backed securities & collateralized mortgage obligations | Estimated Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Investment securities available-for-sale	1,184,053	1,239,851
U.S. agency residential mortgage-backed securities & collateralized mortgage obligations | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Investment securities available-for-sale	0	0
U.S. agency residential mortgage-backed securities & collateralized mortgage obligations | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Investment securities available-for-sale	1,184,053	1,239,851
U.S. agency residential mortgage-backed securities & collateralized mortgage obligations | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Investment securities available-for-sale	0	0
Private mortgage-backed securities | Estimated Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Investment securities available-for-sale	415	551
Private mortgage-backed securities | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Investment securities available-for-sale	0	0
Private mortgage-backed securities | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Investment securities available-for-sale	415	551
Private mortgage-backed securities | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Investment securities available-for-sale	$ 0	$ 0