Fair Values Measurements and Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014	Jun. 30, 2014
Securities Available for Sale [Abstract]
Total Securities Available for Sale	$ 1,129,249	$ 1,013,171
Trading Securities	8,468	7,793
Liabilities [Abstract]
Allowance for loan and lease losses collateral dependent impaired loans with specific reserves	$ 2,900		$ 2,100
Liquidation expense ratio on impaired collateral minimum (in hundredths)	10.00%
Liquidation expense ratio on impaired collateral maximum (in hundredths)	35.00%
Financial assets [Abstract]
Securities held to maturity	$ 454,255	454,994
Financial liabilities [Abstract]
Time deposits	948,154	1,043,823
Long-term debt	130,705	130,945
Junior subordinated debt	101,196	101,196
Carrying Amount [Member] | Significant Other Observable Inputs (Level 2) [Member]
Financial assets [Abstract]
Securities held to maturity	454,312	454,361
Financial liabilities [Abstract]
Time deposits	948,154	1,043,823
Long-term debt	130,705	130,945
Junior subordinated debt	101,196	101,196
Carrying Amount [Member] | Significant Unobservable Inputs (Level 3) [Member]
Financial assets [Abstract]
Net Loans	5,705,929	5,528,912
Estimated Fair Value [Member] | Significant Other Observable Inputs (Level 2) [Member]
Financial assets [Abstract]
Securities held to maturity	454,255	454,994
Financial liabilities [Abstract]
Time deposits	942,611	1,038,877
Long-term debt	132,559	132,562
Junior subordinated debt	95,977	103,770
Estimated Fair Value [Member] | Significant Unobservable Inputs (Level 3) [Member]
Financial assets [Abstract]
Net Loans	5,728,903	5,584,777
Recurring Basis [Member]
Securities Available for Sale [Abstract]
U.S. Treasury	10,014	23,111
Federal Agency	396,923	329,914
State & municipal	30,360	37,570
Mortgage-backed	354,829	364,727
Collateralized mortgage obligations	321,523	242,129
Other securities	15,600	15,720
Total Securities Available for Sale	1,129,249	1,013,171
Trading Securities	8,468	7,793
Interest Rate Swaps	4,703	4,707
Total	1,142,420	1,025,671
Liabilities [Abstract]
Interest Rate Swaps	4,703	4,707
Total	4,703	4,707
Recurring Basis [Member] | Quoted Prices in Active Market for Identical Assets (Level I) [Member]
Securities Available for Sale [Abstract]
U.S. Treasury	10,014	23,111
Federal Agency	0	0
State & municipal	0	0
Mortgage-backed	0	0
Collateralized mortgage obligations	0	0
Other securities	7,740	7,612
Total Securities Available for Sale	17,754	30,723
Trading Securities	8,468	7,793
Interest Rate Swaps	0	0
Total	26,222	38,516
Liabilities [Abstract]
Interest Rate Swaps	0	0
Total	0	0
Recurring Basis [Member] | Significant Other Observable Inputs (Level 2) [Member]
Securities Available for Sale [Abstract]
U.S. Treasury	0	0
Federal Agency	396,923	329,914
State & municipal	30,360	37,570
Mortgage-backed	354,829	364,727
Collateralized mortgage obligations	321,523	242,129
Other securities	7,860	8,108
Total Securities Available for Sale	1,111,495	982,448
Trading Securities	0	0
Interest Rate Swaps	4,703	4,707
Total	1,116,198	987,155
Liabilities [Abstract]
Interest Rate Swaps	4,703	4,707
Total	4,703	4,707
Recurring Basis [Member] | Significant Unobservable Inputs (Level 3) [Member]
Securities Available for Sale [Abstract]
U.S. Treasury	0	0
Federal Agency	0	0
State & municipal	0	0
Mortgage-backed	0	0
Collateralized mortgage obligations	0	0
Other securities	0	0
Total Securities Available for Sale	0	0
Trading Securities	0	0
Interest Rate Swaps	0	0
Total	0	0
Liabilities [Abstract]
Interest Rate Swaps	0	0
Total	0	$ 0
Nonrecurring Basis [Member]
Liabilities [Abstract]
Collateral dependent impaired financing receivable with specific reserves	$ 8,700		$ 9,000