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	Jun. 30, 2013	Dec. 31, 2012
Fair Value Of Other Financial Instrument [Line Items]
Impaired and nonaccrual loans	$ 26,605	$ 27,796
Other real estate	1,149	1,366
Total assets at fair value on a nonrecurring basis	27,754	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	26,605	27,796
Other real estate	1,149	1,366
Total assets at fair value on a nonrecurring basis	$ 27,754	$ 29,162