Fair Value Measurements and Fair Value of Financial Instruments (Details) (USD $)	Mar. 31, 2013	Dec. 31, 2012
Securities Available for Sale [Abstract]
Total Securities Available for Sale	$ 1,465,791,000	$ 1,147,999,000
Trading Securities	4,762,000	3,918,000
Liabilities [Abstract]
Collateral dependent impaired financing receivable with specific reserves	4,100,000	8,400,000
Allowance for loan and lease losses collateral dependent impaired loans with specific reserves	600,000	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%
Financial liabilities [Abstract]
Time deposits	1,166,480,000	983,261,000
Long-term debt	428,661,000	367,492,000
Trust preferred debentures	101,196,000	75,422,000
Fair Value, Inputs, Level 2 [Member] | Carrying Amount [Member]
Financial assets [Abstract]
Securities held to maturity	62,474,000	60,563,000
Financial liabilities [Abstract]
Time deposits	1,166,480,000	983,261,000
Long-term debt	428,661,000	367,492,000
Trust preferred debentures	101,196,000	75,422,000
Fair Value, Inputs, Level 2 [Member] | Estimated Fair Value [Member]
Financial assets [Abstract]
Securities held to maturity	63,361,000	61,535,000
Financial liabilities [Abstract]
Time deposits	1,178,242,000	994,376,000
Long-term debt	468,095,000	407,404,000
Trust preferred debentures	100,460,000	74,147,000
Fair Value, Inputs, Level 3 [Member] | Carrying Amount [Member]
Financial assets [Abstract]
Net Loans	5,126,299,000	4,208,282,000
Fair Value, Inputs, Level 3 [Member] | Estimated Fair Value [Member]
Financial assets [Abstract]
Net Loans	5,226,708,000	4,313,244,000
Fair Value, Measurements, Recurring [Member]
Securities Available for Sale [Abstract]
U.S. Treasury	69,225,000	64,425,000
Federal Agency	297,373,000	282,814,000
State & municipal	146,252,000	86,802,000
Mortgage-backed	345,348,000	250,281,000
Collateralized mortgage obligations	591,738,000	449,723,000
Other securities	15,855,000	13,954,000
Total Securities Available for Sale	1,465,791,000	1,147,999,000
Trading Securities	4,762,000	3,918,000
Interest Rate Swaps	1,594,000	1,490,000
Total	1,472,147,000	1,153,407,000
Liabilities [Abstract]
Interest Rate Swaps	1,594,000	1,490,000
Total	1,594,000	1,490,000
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Securities Available for Sale [Abstract]
U.S. Treasury	69,225,000	64,425,000
Federal Agency	0	0
State & municipal	0	0
Mortgage-backed	0	0
Collateralized mortgage obligations	0	0
Other securities	10,643,000	11,866,000
Total Securities Available for Sale	79,868,000	76,291,000
Trading Securities	4,762,000	3,918,000
Interest Rate Swaps	0	0
Total	84,630,000	80,209,000
Liabilities [Abstract]
Interest Rate Swaps	0	0
Total	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Securities Available for Sale [Abstract]
U.S. Treasury	0	0
Federal Agency	297,373,000	282,814,000
State & municipal	146,252,000	86,802,000
Mortgage-backed	345,348,000	250,281,000
Collateralized mortgage obligations	591,738,000	449,723,000
Other securities	5,212,000	2,088,000
Total Securities Available for Sale	1,385,923,000	1,071,708,000
Trading Securities	0	0
Interest Rate Swaps	1,594,000	1,490,000
Total	1,387,517,000	1,073,198,000
Liabilities [Abstract]
Interest Rate Swaps	1,594,000	1,490,000
Total	1,594,000	1,490,000
Fair Value, Measurements, Recurring [Member] | Fair Value, 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