Fair Value Measurements (Details 3) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011	Jun. 30, 2011	Dec. 31, 2010
Estimated fair values of company's financial instruments
Cash and Cash Equivalents	$ 1,763,908	$ 1,707,733	$ 1,571,099	$ 1,204,079
Securities held for investment	19,734
Total loans (net of unearned interest)	3,065,439	3,013,498	2,861,844
Allowance for loan losses	(37,436)	(37,656)	(37,092)
Loans, net	3,028,003	2,975,842	2,824,752
Deposits	5,099,648	5,037,735	4,701,999
Short-term borrowings	6,340	8,274	1,400
Long-term borrowings	11,329	18,476	32,121
Junior subordinated notes	26,804	36,083	28,866
Carrying Amount [Member]
Estimated fair values of company's financial instruments
Cash and Cash Equivalents	1,763,908		1,571,199
Securities held for investment	19,734		25,654
Total loans (net of unearned interest)	3,065,439		2,861,844
Allowance for loan losses	(37,436)		(37,092)
Loans, net	3,028,003		2,824,752
Deposits	5,099,648		4,701,999
Short-term borrowings	6,340		1,400
Long-term borrowings	11,329		32,121
Junior subordinated notes	26,804		28,866
Estimated Market Value [Member]
Estimated fair values of company's financial instruments
Cash and Cash Equivalents	1,763,908		1,571,199
Securities held for investment	20,104		26,225
Loans, net	3,092,725		2,843,098
Deposits	5,121,335		4,732,880
Short-term borrowings	6,340		1,400
Long-term borrowings	11,431		32,620
Junior subordinated notes	28,970		31,997
Loan commitments	1,321		1,058
Letters of credit	$ 428		$ 441