Summary of Significant Accounting Policies - Basic and Diluted Earnings 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
Accounting Policies [Abstract]
Net Income	$ 4,869	[1]	$ 3,813	$ 4,123	[1]	$ 3,360	$ 3,289	$ 2,991	$ 2,830	$ 2,828	$ 16,165	$ 11,938	$ 8,372
Weighted average number of shares outstanding, basic (in shares)											15,172	14,968	14,697
Earnings per share, basic (in dollars per share)	$ 0.32	[1]	$ 0.25	$ 0.27	[1]	$ 0.22	$ 0.22	$ 0.20	$ 0.19	$ 0.19	$ 1.07	$ 0.80	$ 0.57
Number of shares, attribuatable to equity based compensation plans (in shares)											1,669	1,763	1,376
Dilutive effect on basic earnings per share (in dollars per share)											$ (0.11)	$ (0.09)	$ (0.05)
Weighted average number of shares outstanding, diluted (in shares)											16,841	16,731	16,073
Earnings per share, diluted (in dollars per share)	$ 0.29	[1]	$ 0.23	$ 0.25	[1]	$ 0.20	$ 0.20	$ 0.18	$ 0.17	$ 0.17	$ 0.96	$ 0.71	$ 0.52

[1] Included in interest and other income is $0.4 million or $0.03 basic and diluted net income per share, and $0.8 million or $0.05 basic and diluted net income per share in the second and fourth quarters, respectively, for life insurance proceeds received for former Company executives that passed away during the respective quarters.