Fair Values Measurements and Fair Value of Financial Instruments (Details) (USD $)	Mar. 31, 2014	Dec. 31, 2013
Securities Available for Sale [Abstract]
Total Securities Available for Sale	$ 1,377,585,000	$ 1,364,881,000
Trading Securities	6,954,000	5,779,000
Liabilities [Abstract]
Collateral dependent impaired financing receivable with specific reserves	4,000,000	5,000,000
Allowance for loan and lease losses collateral dependent impaired loans with specific reserves	900,000	700,000
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	114,920,000	113,276,000
Financial liabilities [Abstract]
Time deposits	969,361,000	1,021,142,000
Long-term debt	308,679,000	308,823,000
Junior subordinated debt	101,196,000	101,196,000
Significant Other Observable Inputs (Level 2) [Member] | Carrying Amount [Member]
Financial assets [Abstract]
Securities held to maturity	117,896,000	117,283,000
Financial liabilities [Abstract]
Time deposits	969,361,000	1,021,142,000
Long-term debt	308,679,000	308,823,000
Junior subordinated debt	101,196,000	101,196,000
Significant Other Observable Inputs (Level 2) [Member] | Estimated Fair Value [Member]
Financial assets [Abstract]
Securities held to maturity	114,920,000	113,276,000
Financial liabilities [Abstract]
Time deposits	969,980,000	1,023,982,000
Long-term debt	323,712,000	325,195,000
Junior subordinated debt	105,864,000	105,121,000
Significant Unobservable Inputs (Level 3) [Member] | Carrying Amount [Member]
Financial assets [Abstract]
Net Loans	5,412,591,000	5,337,361,000
Significant Unobservable Inputs (Level 3) [Member] | Estimated Fair Value [Member]
Financial assets [Abstract]
Net Loans	5,460,326,000	5,386,520,000
Recurring Basis [Member]
Securities Available for Sale [Abstract]
U.S. Treasury	33,473,000	43,616,000
Federal Agency	300,158,000	278,915,000
State & municipal	112,695,000	113,665,000
Mortgage-backed	378,158,000	364,164,000
Collateralized mortgage obligations	537,647,000	549,528,000
Other securities	15,454,000	14,993,000
Total Securities Available for Sale	1,377,585,000	1,364,881,000
Trading Securities	6,954,000	5,779,000
Interest Rate Swaps	1,283,000	281,000
Total	1,385,822,000	1,370,941,000
Liabilities [Abstract]
Interest Rate Swaps	1,283,000	281,000
Total	1,283,000	281,000
Recurring Basis [Member] | Quoted Prices in Active Market for Identical Assets (Level I) [Member]
Securities Available for Sale [Abstract]
U.S. Treasury	33,473,000	43,616,000
Federal Agency	0	0
State & municipal	0	0
Mortgage-backed	0	0
Collateralized mortgage obligations	0	0
Other securities	7,238,000	6,796,000
Total Securities Available for Sale	40,711,000	50,412,000
Trading Securities	6,954,000	5,779,000
Interest Rate Swaps	0	0
Total	47,665,000	56,191,000
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	300,158,000	278,915,000
State & municipal	112,695,000	113,665,000
Mortgage-backed	378,158,000	364,164,000
Collateralized mortgage obligations	537,647,000	549,528,000
Other securities	8,216,000	8,197,000
Total Securities Available for Sale	1,336,874,000	1,314,469,000
Trading Securities	0	0
Interest Rate Swaps	1,283,000	281,000
Total	1,338,157,000	1,314,750,000
Liabilities [Abstract]
Interest Rate Swaps	1,283,000	281,000
Total	1,283,000	281,000
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