Fair Value Measurements (Balances of Assets and Liabilities Measured At Fair Value on a Recurring Basis) (Details) (USD $) In Thousands	Jun. 30, 2011	Dec. 31, 2010
Assets measured at fair value, available for sale securities	$ 820,847	$ 738,125
Derivative financial instruments	29,333	25,631
Assets measured at fair value, Total	850,180	763,756
Derivative financial instruments	29,326	25,043
Liabilities measured at fair value, Total	29,326	25,043
Available for Sale Debt Securities [Member]
Assets measured at fair value, available for sale securities	818,960	735,936
Available for Sale Debt Securities [Member] | Level 2 [Member]
Assets measured at fair value, available for sale securities	806,409	718,717
Available for Sale Debt Securities [Member] | Level 2 [Member] | U.S. Treasury and Other U.S. Government Agencies and Corporations [Member]
Assets measured at fair value, available for sale securities	333,284	300,568
Available for Sale Debt Securities [Member] | Level 2 [Member] | Agency Mortgage-Backed Securities [Member]
Assets measured at fair value, available for sale securities	241,148	211,507
Available for Sale Debt Securities [Member] | Level 2 [Member] | Agency Collateralized Mortgage Obligations [Member]
Assets measured at fair value, available for sale securities	186,985	147,866
Available for Sale Debt Securities [Member] | Level 2 [Member] | Non-Agency Collateralized Mortgage Obligations [Member]
Assets measured at fair value, available for sale securities	35	38
Available for Sale Debt Securities [Member] | Level 2 [Member] | States Of The U.S. And Political Subdivisions [Member]
Assets measured at fair value, available for sale securities	44,957	58,738
Available for Sale Debt Securities [Member] | Level 3 [Member]
Assets measured at fair value, available for sale securities	12,551	17,219
Available for Sale Debt Securities [Member] | Level 3 [Member] | Collateralized Debt Obligations [Member]
Assets measured at fair value, available for sale securities	6,605	5,974
Available for Sale Debt Securities [Member] | Level 3 [Member] | Other Debt Securities [Member]
Assets measured at fair value, available for sale securities	5,946	11,245
Available for Sale Debt Securities [Member] | U.S. Treasury and Other U.S. Government Agencies and Corporations [Member]
Assets measured at fair value, available for sale securities	333,284	300,568
Available for Sale Debt Securities [Member] | Agency Mortgage-Backed Securities [Member]
Assets measured at fair value, available for sale securities	241,148	211,507
Available for Sale Debt Securities [Member] | Agency Collateralized Mortgage Obligations [Member]
Assets measured at fair value, available for sale securities	186,985	147,866
Available for Sale Debt Securities [Member] | Non-Agency Collateralized Mortgage Obligations [Member]
Assets measured at fair value, available for sale securities	35	38
Available for Sale Debt Securities [Member] | States Of The U.S. And Political Subdivisions [Member]
Assets measured at fair value, available for sale securities	44,957	58,738
Available for Sale Debt Securities [Member] | Collateralized Debt Obligations [Member]
Assets measured at fair value, available for sale securities	6,605	5,974
Available for Sale Debt Securities [Member] | Other Debt Securities [Member]
Assets measured at fair value, available for sale securities	5,946	11,245
Available for Sale Equity Securities [Member]
Assets measured at fair value, available for sale securities	1,887	2,189
Available for Sale Equity Securities [Member] | Level 1 [Member]
Assets measured at fair value, available for sale securities	409	501
Available for Sale Equity Securities [Member] | Level 1 [Member] | Financial Services Industry [Member]
Assets measured at fair value, available for sale securities	375	470
Available for Sale Equity Securities [Member] | Level 1 [Member] | Insurance Services Industry [Member]
Assets measured at fair value, available for sale securities	34	31
Available for Sale Equity Securities [Member] | Level 2 [Member]
Assets measured at fair value, available for sale securities	1,011	1,313
Available for Sale Equity Securities [Member] | Level 2 [Member] | Financial Services Industry [Member]
Assets measured at fair value, available for sale securities	1,011	1,313
Available for Sale Equity Securities [Member] | Level 3 [Member]
Assets measured at fair value, available for sale securities	467	375
Available for Sale Equity Securities [Member] | Level 3 [Member] | Financial Services Industry [Member]
Assets measured at fair value, available for sale securities	467	375
Available for Sale Equity Securities [Member] | Financial Services Industry [Member]
Assets measured at fair value, available for sale securities	1,853	2,158
Available for Sale Equity Securities [Member] | Insurance Services Industry [Member]
Assets measured at fair value, available for sale securities	34	31
Level 1 [Member]
Assets measured at fair value, available for sale securities	409	501
Assets measured at fair value, Total	409	501
Level 2 [Member]
Assets measured at fair value, available for sale securities	807,420	720,030
Derivative financial instruments	29,333	25,631
Assets measured at fair value, Total	836,753	745,661
Derivative financial instruments	29,326	25,043
Liabilities measured at fair value, Total	29,326	25,043
Level 3 [Member]
Assets measured at fair value, available for sale securities	13,018	17,594
Assets measured at fair value, Total	$ 13,018	$ 17,594