Fair Value of Assets and Liabilities (Summary of Balances of Assets and Liabilities Measured at Fair Value on a Recurring Basis) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities	$ 1,724,667	$ 1,716,388
Trading account securities	1,989	448
Mortgage loans held-for-sale	418,374	388,038
Mortgage servicing rights	19,103	9,092	$ 8,435	$ 8,946
Derivative assets	49,213	42,779
Derivative liabilities	37,665	42,458
U.S. Treasury
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities	141,983	306,729
US Government agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities	189,152	70,236
Municipal
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities	131,809	108,595
Mortgage-backed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities	1,161,084	1,092,597
Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities	35,248	56,686
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading account securities	1,989	448
Mortgage loans held-for-sale	418,374	388,038
Loans held-for-investment	22,137	11,361
Mortgage servicing rights	19,103	9,092
Nonqualified deferred compensation assets	9,228	8,517
Derivative assets	56,394	51,298
Total	2,251,892	2,185,142
Derivative liabilities	39,839	45,019
Fair Value, Measurements, Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading account securities	1,989	448
Mortgage loans held-for-sale	418,374	388,038
Loans held-for-investment	0	11,361
Mortgage servicing rights	0	0
Nonqualified deferred compensation assets	9,228	8,517
Derivative assets	54,103	44,277
Total	2,128,735	2,075,217
Derivative liabilities	39,839	45,019
Fair Value, Measurements, Recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading account securities	0	0
Mortgage loans held-for-sale	0	0
Loans held-for-investment	22,137	0
Mortgage servicing rights	19,103	9,092
Nonqualified deferred compensation assets	0	0
Derivative assets	2,291	7,021
Total	123,157	109,925
Derivative liabilities	0	0
Fair Value, Measurements, Recurring | U.S. Treasury
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities	141,983	306,729
Fair Value, Measurements, Recurring | U.S. Treasury | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities	141,983	306,729
Fair Value, Measurements, Recurring | U.S. Treasury | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities	0	0
Fair Value, Measurements, Recurring | US Government agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities	189,152	70,236
Fair Value, Measurements, Recurring | US Government agencies | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities	189,152	70,236
Fair Value, Measurements, Recurring | US Government agencies | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities	0	0
Fair Value, Measurements, Recurring | Municipal
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities	131,809	108,595
Fair Value, Measurements, Recurring | Municipal | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities	52,183	39,982
Fair Value, Measurements, Recurring | Municipal | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities	79,626	68,613
Fair Value, Measurements, Recurring | Corporate notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities	65,391	81,545
Fair Value, Measurements, Recurring | Corporate notes | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities	65,391	81,545
Fair Value, Measurements, Recurring | Corporate notes | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities	0	0
Fair Value, Measurements, Recurring | Mortgage-backed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities	1,161,084	1,092,597
Fair Value, Measurements, Recurring | Mortgage-backed | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities	1,161,084	1,092,597
Fair Value, Measurements, Recurring | Mortgage-backed | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities	0	0
Fair Value, Measurements, Recurring | Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities	35,248	56,686
Fair Value, Measurements, Recurring | Equity securities | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities	35,248	31,487
Fair Value, Measurements, Recurring | Equity securities | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities	$ 0	$ 25,199