Income Taxes - Provision for Federal and State Income Tax (Details) (USD $) In Thousands, 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	Dec. 31, 2010
Current:
Federal									$ 2,753	$ 2,829	$ 5,142
State									258	334	387
Deferred:
Federal									2,397	1,480	(2,162)
State									143	133	(85)
Provision for federal and state income taxes, total	$ 1,358	$ 1,842	$ 1,405	$ 946	$ 1,349	$ 1,402	$ 1,199	$ 826	$ 5,551	$ 4,776	$ 3,282