Estimated Fair Value of Financial Instruments - Balances of Assets and Liabilities Measured at Fair Value on a Nonrecurring Basis (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Fair Value Of Other Financial Instrument [Line Items]
Impaired and nonaccrual loans	$ 28,514	$ 27,796
Other real estate	1,215	1,366
Total assets at fair value on a nonrecurring basis	29,729	29,162
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair Value Of Other Financial Instrument [Line Items]
Impaired and nonaccrual loans	0	0
Other real estate	0	0
Total assets at fair value on a nonrecurring basis	0	0
Significant Other Observable Inputs (Level 2) [Member]
Fair Value Of Other Financial Instrument [Line Items]
Impaired and nonaccrual loans	0	0
Other real estate	0	0
Total assets at fair value on a nonrecurring basis	0	0
Significant Unobservable Inputs (Level 3) [Member]
Fair Value Of Other Financial Instrument [Line Items]
Impaired and nonaccrual loans	28,514	27,796
Other real estate	1,215	1,366
Total assets at fair value on a nonrecurring basis	$ 29,729	$ 29,162