Fair Value (Narrative) (Details) (USD $)	3 Months Ended		12 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012	Dec. 31, 2011
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Impaired Financing Receivable, Carrying Value	$ 130,300,000		$ 137,200,000
Discount percentage applied to real estate appraised values	15.00%
Discount percentage applied to lot development appraised values	6.00%
Partial Charge-Offs On Impaired Loans	102,900,000		105,100,000
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	8,260,000		8,276,000
Impaired Financing Receivable, Related Allowance	8,260,000		8,276,000
Impaired loans carried at fair value	51,271,000		53,900,000
Partial Charge-Offs On Impaired Loans carried at Fair Value	89,300,000		91,600,000
Book value of impaired loans carried at fair value	56,000,000		59,000,000
Remaining amount of impaired loans carried at cost	74,300,000		78,200,000
Impaired Financing Receivable, carried at fair value, related expense	2,300,000	4,400,000
MSR recorded at lower of cost or fair value	8,121,000	8,975,000	7,763,000	9,301,000
Mortgage Servicing Rights Fair Value	5,900,000
Valuation allowance of MSR	2,262,000	1,021,000	2,324,000	1,021,000
MSRs recorded at cost	2,200,000
Changes due to fair value adjustments	(62,000)	0	0
Other Real Estate, Foreclosed Assets, and Repossessed Assets, Fair Value	18,300,000		19,900,000
OREO valuation adjustments	(401,000)	1,359,000
Commercial Receivables, excluding Commercial, Financial, and Agricultural [Domain]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Impaired Financing Receivable, Related Allowance	4,740,000		5,100,000
Financing Receivable, not collateral dependent [Domain]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Impaired Financing Receivable, Related Allowance	$ 3,620,000		$ 3,176,000