Earnings Per Share - Computation of earning per share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011
Basic earnings per share
Income available to common stockholders (in dollars)									$ 3,650	$ 1,410
Income available to common stockholders (in shares)									1,517,902	1,514,472
Income available to common stockholders (in dollars per share)	$ 1.17	$ 0.50	$ 0.40	$ 0.33	$ 0.31	$ (0.20)	$ 0.35	$ 0.47	$ 2.40	$ 0.93
Effect of dilutive RRP awards and stock options (in shares)									2,005	1,974
Diluted earnings per share
Income available to common stockholders and assumed conversions (in dollars)									$ 3,650	$ 1,410
Income available to common stockholders and assumed conversions (in shares)									1,519,907	1,516,446
Income available to common stockholders and assumed conversions (in dollars per share)	$ 1.17	$ 0.50	$ 0.40	$ 0.33	$ 0.31	$ (0.20)	$ 0.35	$ 0.47	$ 2.40	$ 0.93