Significant Accounting Policies (Details) (USD $) Share data in Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Business, Basis of Financial Statement Presentation and Principles of Consolidation [Abstract]
Number of offices	over 150
Loans Held-for-sale [Abstract]
Percentage of remaining principal balance of the loan servicer may repurchase (in hundredths)	100.00%
Serviced loans purchased from GNMA, value		$ 53,900,000
Unpaid principal balance of GNMA loans eligible for repurchase	58,800,000	29,700,000	81,000,000
Loans [Abstract]
Number of days loan is contractually past due to be classified as a past due loan (in days)	30 D
Balance of commercial nonaccrual loans identified for impairment analysis, minimum	500,000
Allowance for loan losses [Abstract]
Methodology elements in allowance for loan losses guidance	3
Number of classifications of commercial loans with common risk characteristics	13
Key market regions	4
Federal Home Loan Bank and Federal Reserve stock
Securities with limited marketability	31,800,000	40,700,000
Identifiable intangible assets [Abstract]
Finite-lived intangible assets, average useful life (in years)	20
Statement of cash flows specific transaction amounts [Abstract]
Income taxes paid	37,604,000	53,628,000	60,456,000
Interest expense paid on deposits and borrowings	44,060,000	59,858,000	93,402,000
Noncash transfers from loans to foreclosed properties	57,297,000	61,786,000	78,300,000
Transfer of long-term FHLB advance to short-term	0	75,000,000	0
Assets acquired in business combination	207,243,000	0	0
Liabilities assumed in business combination	$ 228,236,000	$ 0	$ 0
Weighted-average shares used to calculate basic and diluted EPS [Abstract]
Basic shares (in shares)	64,066	63,849	57,834
Dilutive shares (in shares)	195	190	102
Diluted shares (in shares)	64,261	64,039	57,936
Weighted-average antidilutive shares (in shares)	1,226	1,259	1,552
Buildings [Member]
Premises and Equipment, Net [Abstract]
Estimated useful lives of the assets, maximum (in years)	39
Furniture and Fixtures [Member]
Premises and Equipment, Net [Abstract]
Estimated useful lives of the assets, maximum (in years)	10
Estimated useful lives of the assets, minimum (in years)	3
Commercial Credits [Member]
Loans [Abstract]
Number of days past due on credits for loan to be classified as nonaccrual (in days)	90 D
Non-Business Purpose Credits [Member]
Loans [Abstract]
Number of days past due on credits for loan to be classified as nonaccrual (in days)	120 D
Consumer Loans [Member]
Loans [Abstract]
Number of days past due loans are generally charged-off (in days)	180 D
Non-real Estate Consumer Purpose Loans [Member]
Loans [Abstract]
Number of days past due loans are generally charged-off (in days)	120 D
Credit Card Loans [Member]
Loans [Abstract]
Number of days past due loans are generally charged-off (in days)	180 D