Fair Values Measurements and Fair Value of Financial Instruments (Details) (USD $)	Sep. 30, 2013	Dec. 31, 2012
Securities Available for Sale [Abstract]
Total Securities Available for Sale	$ 1,385,734,000	$ 1,147,999,000
Trading Securities	5,285,000	3,918,000
Liabilities [Abstract]
Collateral dependent impaired financing receivable with specific reserves	6,200,000	8,400,000
Allowance for loan and lease losses collateral dependent impaired loans with specific reserves	1,100,000	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 assets [Abstract]
Securities held to maturity	115,620,000	61,535,000
Financial liabilities [Abstract]
Time deposits	1,063,730,000	983,261,000
Long-term debt	309,009,000	367,492,000
Trust preferred debentures	101,196,000	75,422,000
Significant Other Observable Inputs (Level 2) [Member] | Carrying Amount [Member]
Financial assets [Abstract]
Securities held to maturity	118,259,000	60,563,000
Financial liabilities [Abstract]
Time deposits	1,063,730,000	983,261,000
Long-term debt	309,009,000	367,492,000
Trust preferred debentures	101,196,000	75,422,000
Significant Other Observable Inputs (Level 2) [Member] | Estimated Fair Value [Member]
Financial assets [Abstract]
Securities held to maturity	115,620,000	61,535,000
Financial liabilities [Abstract]
Time deposits	1,068,888,000	994,376,000
Long-term debt	336,128,000	407,404,000
Trust preferred debentures	103,364,000	74,147,000
Significant Unobservable Inputs (Level 3) [Member] | Carrying Amount [Member]
Financial assets [Abstract]
Net Loans	5,297,047,000	4,208,282,000
Significant Unobservable Inputs (Level 3) [Member] | Estimated Fair Value [Member]
Financial assets [Abstract]
Net Loans	5,358,132,000	4,313,244,000
Recurring Basis [Member]
Securities Available for Sale [Abstract]
U.S. Treasury	43,804,000	64,425,000
Federal Agency	295,194,000	282,814,000
State & municipal	118,602,000	86,802,000
Mortgage-backed	335,206,000	250,281,000
Collateralized mortgage obligations	578,210,000	449,723,000
Other securities	14,718,000	13,954,000
Total Securities Available for Sale	1,385,734,000	1,147,999,000
Trading Securities	5,285,000	3,918,000
Interest Rate Swaps	1,038,000	1,490,000
Total	1,392,057,000	1,153,407,000
Liabilities [Abstract]
Interest Rate Swaps	1,038,000	1,490,000
Total	1,038,000	1,490,000
Recurring Basis [Member] | Quoted Prices in Active Market for Identical Assets (Level I) [Member]
Securities Available for Sale [Abstract]
U.S. Treasury	43,804,000	64,425,000
Federal Agency	0	0
State & municipal	0	0
Mortgage-backed	0	0
Collateralized mortgage obligations	0	0
Other securities	9,671,000	11,866,000
Total Securities Available for Sale	53,475,000	76,291,000
Trading Securities	5,285,000	3,918,000
Interest Rate Swaps	0	0
Total	58,760,000	80,209,000
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	295,194,000	282,814,000
State & municipal	118,602,000	86,802,000
Mortgage-backed	335,206,000	250,281,000
Collateralized mortgage obligations	578,210,000	449,723,000
Other securities	5,047,000	2,088,000
Total Securities Available for Sale	1,332,259,000	1,071,708,000
Trading Securities	0	0
Interest Rate Swaps	1,038,000	1,490,000
Total	1,333,297,000	1,073,198,000
Liabilities [Abstract]
Interest Rate Swaps	1,038,000	1,490,000
Total	1,038,000	1,490,000
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