Commitments, Contingencies, and Concentrations (Details) (USD $)	3 Months Ended		12 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012	Dec. 31, 2005
Schedule of Equity Method Investments [Line Items]
Loss contingency accrual	$ 0	$ 1,600,000	$ 2,000,000
Percentage of entity's share in loss contingency (in hundredths)			60.00%
Loss contingency, entity's share amount			1,200,000
Payments To Acquire Collateralized Debt Obligation offered by Lehman Brothers, Inc.				25,000,000
CSL [Member]
Schedule of Equity Method Investments [Line Items]
Percentage of equity interest hold (in hundredths)	60.00%
RTL [Member]
Schedule of Equity Method Investments [Line Items]
Percentage of equity interest hold (in hundredths)	60.00%
Open-end lines of credit [Member]
Contracts of financial instruments represent credit risk [Abstract]
Financial instruments whose contract amounts represent credit risk	23,182,000		20,515,000
Commitments to Extend Credit [Member]
Contracts of financial instruments represent credit risk [Abstract]
Financial instruments whose contract amounts represent credit risk	13,010,000		24,030,000
Standby letters of credit and financial guarantees written [Member]
Contracts of financial instruments represent credit risk [Abstract]
Financial instruments whose contract amounts represent credit risk	$ 1,097,000		$ 1,199,000