Schedule of Financial Assets and Financial Liabilities Measured at Fair Value on a Recurring and Non-Recurring Basis (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Real Estate Acquired Through Foreclosure, Valuation Adjustments	$ 106	$ 0
Related Allowance	7,468		5,792
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value Measured on a Non-recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	0		0
Other real estate owned	0		0
Long-lived assets to be disposed of by sale	0		0
Significant Other Observable Inputs (Level 2) | Fair Value Measured on a Non-recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	0		0
Other real estate owned	0		0
Long-lived assets to be disposed of by sale	0		0
Significant Unobservable Inputs (Level 3) | Fair Value Measured on a Non-recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	35,098		30,494
Other real estate owned	6,499		4,554
Real Estate Acquired Through Foreclosure, Valuation Adjustments	106	0
Long-lived assets to be disposed of by sale	1,083		1,083
Related Allowance	7,468		5,792
Impaired Financing Receivable, Related Allowance, Partial Loan Charge-Offs	8,199		8,760
Obligations of U.S. government agencies | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities available-for-sale	0		0
Obligations of U.S. government agencies | Significant Other Observable Inputs (Level 2) | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities available-for-sale	769,455		720,933
Obligations of U.S. government agencies | Significant Unobservable Inputs (Level 3) | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities available-for-sale	0		0
U.S. agency residential mortgage-backed securities & collateralized mortgage obligations | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
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 Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities available-for-sale	1,007,300		990,666
U.S. agency residential mortgage-backed securities & collateralized mortgage obligations | Significant Unobservable Inputs (Level 3) | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities available-for-sale	0		0
Private mortgage-backed securities | Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities available-for-sale	0		0
Private mortgage-backed securities | Significant Other Observable Inputs (Level 2) | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities available-for-sale	302		325
Private mortgage-backed securities | Significant Unobservable Inputs (Level 3) | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities available-for-sale	0		0
Estimated Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities available-for-sale	1,777,057		1,711,924
Mortgage servicing rights	26,639		21,434
Estimated Fair Value | Fair Value Measured on a Non-recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	35,098		30,494
Other real estate owned	6,499		4,554
Long-lived assets to be disposed of by sale	1,083		1,083
Estimated Fair Value | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities available-for-sale	0		0
Mortgage servicing rights	0		0
Estimated Fair Value | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities available-for-sale	1,777,057		1,711,924
Mortgage servicing rights	26,639		21,434
Estimated Fair Value | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities available-for-sale	0		0
Mortgage servicing rights	0		0
Estimated Fair Value | Significant Unobservable Inputs (Level 3) | Fair Value Measured on a Non-recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	35,098		30,494
Estimated Fair Value | Obligations of U.S. government agencies | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities available-for-sale	769,455		720,933
Estimated Fair Value | U.S. agency residential mortgage-backed securities & collateralized mortgage obligations | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities available-for-sale	1,007,300		990,666
Estimated Fair Value | Private mortgage-backed securities | Fair Value Measured on a Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities available-for-sale	302		325
Carrying Amount
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment securities available-for-sale	1,777,057		1,711,924
Mortgage servicing rights	14,093		14,038
Carrying Amount | Significant Unobservable Inputs (Level 3) | Fair Value Measured on a Non-recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	50,765		45,046
Long-lived assets to be disposed of by sale	1,785		1,785
Change During Period | Fair Value Measured on a Non-recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-lived assets to be disposed of by sale	$ 702		$ 702