Fair Value Measurements and Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015	Jun. 30, 2015
Securities Available for Sale [Abstract]
Total Securities Available for Sale	$ 1,271,596	$ 1,174,544
Trading Securities	$ 8,591	8,377
Liabilities [Abstract]
Liquidation expense ratio on impaired collateral minimum	10.00%
Liquidation expense ratio on impaired collateral maximum	35.00%
Financial assets [Abstract]
Securities held to maturity	$ 512,349	473,140
Financial liabilities [Abstract]
Time deposits	882,712	908,827
Long-term debt	110,306	130,447
Junior subordinated debt	101,196	101,196
Not Designated as Hedging Instrument [Member] | Interest Rate Swaps [Member] | Other Assets [Member]
Derivatives, Fair Value [Line Items]
Fair value of derivative asset	17,800	6,200
Not Designated as Hedging Instrument [Member] | Interest Rate Swaps [Member] | Other Liabilities [Member]
Derivatives, Fair Value [Line Items]
Fair value of derivative liability	17,800	6,200
Not Designated as Hedging Instrument [Member] | Interest Rate Swaps [Member] | Customer Derivative Agreement [Member]
Derivatives, Fair Value [Line Items]
Notional amount	288,100	192,600
Not Designated as Hedging Instrument [Member] | Interest Rate Swaps [Member] | Offsetting Derivative Counterparty Positions [Member]
Derivatives, Fair Value [Line Items]
Notional amount	288,100	192,600
Designated as Hedging Instrument [Member] | Cash Flow Hedging [Member] | Interest Rate Swaps [Member]
Derivatives, Fair Value [Line Items]
Notional amount	150,000
Designated as Hedging Instrument [Member] | Cash Flow Hedging [Member] | Interest Rate Swaps [Member] | Other Liabilities [Member]
Derivatives, Fair Value [Line Items]
Fair value of derivative liability	100
Carrying Amount [Member] | Significant Other Observable Inputs (Level 2) [Member]
Financial assets [Abstract]
Securities held to maturity	500,840	471,031
Financial liabilities [Abstract]
Time deposits	882,712	908,827
Long-term debt	110,306	130,447
Junior subordinated debt	101,196	101,196
Carrying Amount [Member] | Significant Unobservable Inputs (Level 3) [Member]
Financial assets [Abstract]
Net loans	5,974,825	5,820,115
Estimated Fair Value [Member] | Significant Other Observable Inputs (Level 2) [Member]
Financial assets [Abstract]
Securities held to maturity	512,349	473,140
Financial liabilities [Abstract]
Time deposits	886,047	903,501
Long-term debt	111,968	131,268
Junior subordinated debt	96,583	97,346
Estimated Fair Value [Member] | Significant Unobservable Inputs (Level 3) [Member]
Financial assets [Abstract]
Net loans	6,136,103	5,958,427
Recurring Basis [Member]
Securities Available for Sale [Abstract]
Federal Agency	266,835	311,272
State & municipal	37,630	31,637
Mortgage-backed	396,685	409,896
Collateralized mortgage obligations	551,638	404,971
Other securities	18,808	16,768
Total Securities Available for Sale	1,271,596	1,174,544
Trading Securities	8,591	8,377
Interest Rate Swaps	17,775	6,224
Total	1,297,962	1,189,145
Liabilities [Abstract]
Interest Rate Swaps	17,838	6,224
Total	17,838	6,224
Recurring Basis [Member] | Quoted Prices in Active Market for Identical Assets (Level I) [Member]
Securities Available for Sale [Abstract]
Federal Agency	0	0
State & municipal	0	0
Mortgage-backed	0	0
Collateralized mortgage obligations	0	0
Other securities	9,458	7,526
Total Securities Available for Sale	9,458	7,526
Trading Securities	8,591	8,377
Interest Rate Swaps	0	0
Total	18,049	15,903
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]
Federal Agency	266,835	311,272
State & municipal	37,630	31,637
Mortgage-backed	396,685	409,896
Collateralized mortgage obligations	551,638	404,971
Other securities	9,350	9,242
Total Securities Available for Sale	1,262,138	1,167,018
Trading Securities	0	0
Interest Rate Swaps	17,775	6,224
Total	1,279,913	1,173,242
Liabilities [Abstract]
Interest Rate Swaps	17,838	6,224
Total	17,838	6,224
Recurring Basis [Member] | Significant Unobservable Inputs (Level 3) [Member]
Securities Available for Sale [Abstract]
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	9,600		$ 8,700
Allowance for loan and lease losses collateral dependent impaired loans with specific reserves	$ 3,200		$ 2,900