Fair Value of Financial Instruments, Part 2 (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012	Dec. 31, 2011
Financial assets [Abstract]
Cash and cash equivalents	$ 444,774	$ 544,016	$ 525,481	$ 532,943
Securities available for sale	1,077,484	912,092
Held to maturity securities	125,080	151,126
Net loans	2,758,067	2,771,705
Accrued interest receivable	12,475	11,752
Financial liabilities [Abstract]
Demand deposits	298,243	300,544
Interest bearing deposits	3,560,485	3,505,833
Short-term borrowings	171,019	159,846
Accrued interest payable	456	449
Level 1 [Member]
Financial assets [Abstract]
Cash and cash equivalents	444,774	544,016
Securities available for sale	10	10
Held to maturity securities	0	0
Net loans	0	0
Accrued interest receivable	0	0
Financial liabilities [Abstract]
Demand deposits	298,243	300,544
Interest bearing deposits	2,448,880	2,426,170
Short-term borrowings	0	0
Accrued interest payable	108	103
Level 2 [Member]
Financial assets [Abstract]
Cash and cash equivalents	0	0
Securities available for sale	1,077,474	912,082
Held to maturity securities	125,080	151,126
Net loans	0	0
Accrued interest receivable	4,636	4,114
Financial liabilities [Abstract]
Demand deposits	0	0
Interest bearing deposits	1,111,605	1,079,663
Short-term borrowings	171,019	159,846
Accrued interest payable	348	346
Level 3 [Member]
Financial assets [Abstract]
Cash and cash equivalents	0	0
Securities available for sale	0	0
Held to maturity securities	0	0
Net loans	2,758,067	2,771,705
Accrued interest receivable	7,839	7,638
Financial liabilities [Abstract]
Demand deposits	0	0
Interest bearing deposits	0	0
Short-term borrowings	0	0
Accrued interest payable	0	0
Carrying Value [Member]
Financial assets [Abstract]
Cash and cash equivalents	444,774	544,016
Securities available for sale	1,077,484	912,092
Held to maturity securities	117,973	143,426
Federal Reserve Bank and Federal Home Loan Bank stock	9,632	9,632
Net loans	2,656,109	2,636,806
Accrued interest receivable	12,475	11,752
Financial liabilities [Abstract]
Demand deposits	298,243	300,544
Interest bearing deposits	3,559,437	3,503,649
Short-term borrowings	171,019	159,846
Accrued interest payable	$ 456	$ 449