Allowance for Loan Losses Details Textual(Details) (USD $)	3 Months Ended				3 Months Ended				3 Months Ended		12 Months Ended
	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Mar. 31, 2012	Mar. 31, 2013 Covered Loans [Member]	Mar. 31, 2012 Covered Loans [Member]	Dec. 31, 2012 Covered Loans [Member]	Dec. 31, 2011 Covered Loans [Member]	Mar. 31, 2013 Acquired Non Impaired Loans [Member]	Mar. 31, 2012 Acquired Non Impaired Loans [Member]	Dec. 31, 2012 Acquired Non Impaired Loans [Member]	Mar. 31, 2013 Loans with No Related Allowance [Member]
Allowance For Loan And Lease Losses [Line Items]
Loans Due Ninety Days or More or on Nonaccrual Status	90
Loan Commitments	$ 4,068,910,000	$ 4,151,541,000		$ 4,159,112,000								$ 200,000
Minimum Number of Consecutive Payment Cycles After Restructuring Date with Modified Term	6
Loans and Leases Receivable, Allowance, Covered	47,945,000	43,255,000		41,070,000	47,945,000	41,070,000	43,255,000	36,417,000
Minimum Non Performing Substandard Loans Outstanding for Allowance for Credit Losses	300,000
Minimum Non Performing Substandard Doubtful Loans Outstanding for Allowance for Credit Losses	100,000
Provision for Loan Losses Before Benefit Attributable to FDIC Loss Share Agreements					9,677,000	10,831,000
Benefit Attributable to FDIC Loss Share Agreements					(5,539,000)	(4,899,000)
Allowance for Loan and Lease Losses, Provision for Loss, Net									400,000	400,000	300,000
Nonaccrual Non-reaffirmed Bankruptcies	$ 10,000,000	$ 7,700,000	$ 10,600,000