Fair Values of Financial Instruments (Details) (USD $)	Dec. 31, 2012	Dec. 31, 2011
Financial liabilities [Abstract]
Time deposits	$ 983,261,000	$ 933,127,000
Long-term debt	367,492,000	370,344,000
Trust preferred debentures	75,422,000	75,422,000
Securities Available for Sale [Abstract]
Total Securities Available for Sale	1,147,999,000	1,244,619,000
Trading Securities	3,918,000	3,062,000
Liabilities [Abstract]
Collateral dependent impaired loans with no specific reserve	8,400,000
Reserves on collateral dependent impaired loans	2,800,000
Liquidation expense ratio on impaired collateral minimum (in hundredths)	10.00%
Liquidation expense ratio on impaired collateral maximum (in hundredths)	35.00%
Fair Value, Measurements, Recurring [Member]
Securities Available for Sale [Abstract]
U.S. Treasury	64,425,000	82,233,000
Federal Agency	282,814,000	255,846,000
State & municipal	86,802,000	104,789,000
Mortgage-backed	250,281,000	325,397,000
Collateralized mortgage obligations	449,723,000	465,475,000
Other securities	13,954,000	10,879,000
Total Securities Available for Sale	1,147,999,000	1,244,619,000
Trading Securities	3,918,000	3,062,000
Interest Rate Swaps	1,490,000
Total	1,153,407,000	1,247,681,000
Liabilities [Abstract]
Interest Rate Swaps	1,490,000
Total	1,490,000
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Securities Available for Sale [Abstract]
U.S. Treasury	64,425,000	82,233,000
Federal Agency	0	0
State & municipal	0	0
Mortgage-backed	0	0
Collateralized mortgage obligations	0	0
Other securities	11,866,000	8,825,000
Total Securities Available for Sale	76,291,000	91,058,000
Trading Securities	3,918,000	3,062,000
Interest Rate Swaps	0
Total	80,208,000	94,120,000
Liabilities [Abstract]
Interest Rate Swaps	0
Total	0
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Securities Available for Sale [Abstract]
U.S. Treasury	0	0
Federal Agency	282,814,000	255,846,000
State & municipal	86,802,000	104,789,000
Mortgage-backed	250,281,000	325,397,000
Collateralized mortgage obligations	449,723,000	465,475,000
Other securities	2,088,000	2,054,000
Total Securities Available for Sale	1,071,708,000	1,153,561,000
Trading Securities	0	0
Interest Rate Swaps	1,490,000
Total	1,073,198,000	1,153,561,000
Liabilities [Abstract]
Interest Rate Swaps	1,490,000
Total	1,490,000
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [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
Total	0	0
Liabilities [Abstract]
Interest Rate Swaps	0
Total	0
Carrying Amount [Member] | Fair Value, Inputs, Level 2 [Member]
Financial assets [Abstract]
Securities held to maturity	60,563,000	70,811,000
Financial liabilities [Abstract]
Time deposits	983,261,000	933,127,000
Long-term debt	367,492,000	370,344,000
Trust preferred debentures	75,422,000	75,422,000
Carrying Amount [Member] | Fair Value, Inputs, Level 3 [Member]
Financial assets [Abstract]
Net Loans	4,208,282,000	3,728,869,000
Estimated Fair Value [Member] | Fair Value, Inputs, Level 2 [Member]
Financial assets [Abstract]
Securities held to maturity	61,535,000	72,198,000
Financial liabilities [Abstract]
Time deposits	994,376,000	942,437,000
Long-term debt	407,404,000	427,107,000
Trust preferred debentures	74,147,000	75,422,000
Estimated Fair Value [Member] | Fair Value, Inputs, Level 3 [Member]
Financial assets [Abstract]
Net Loans	$ 4,313,244,000	$ 3,821,640,000