Reconciliation of Net Income Per Share (Details) (USD $) In Thousands, except Per 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	Dec. 31, 2010
Summary of Reconciliation of Net Income Per Share
Net income	$ 8,206	$ 3,115	$ 7,038	$ 5,909	$ 4,901	$ 4,702	$ 5,827	$ 5,507	$ 24,268	$ 20,937	$ 6,416
Weighted average shares outstanding	17,044	17,044	17,026	16,961	16,949	16,949	16,864	16,664	17,009	16,817	16,455
Effective of dilutive stock options	106	106	113	114	108	112	255	246	105	136	115
Diluted shares outstanding	17,150	17,150	17,139	17,075	17,057	17,061	17,119	16,910	17,114	16,953	16,570
Basic net income per share	$ 0.48	$ 0.18	$ 0.41	$ 0.35	$ 0.29	$ 0.28	$ 0.35	$ 0.33	$ 1.43	$ 1.24	$ 0.39
Diluted net income per share	$ 0.48	$ 0.18	$ 0.41	$ 0.35	$ 0.29	$ 0.28	$ 0.34	$ 0.33	$ 1.42	$ 1.24	$ 0.39