Net Income per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended												12 Months Ended
	Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Net Income per Share
Net income	$ 9,746	$ 9,459	$ 8,418	$ 8,496	$ 7,345	$ 5,760	$ 5,171	$ 5,368	$ 6,120	$ 5,959	$ 5,834	$ 5,740	$ 36,119	$ 23,644	$ 23,653
Weighted average common shares outstanding - Basic													10,403	10,709	10,845
Plus: Potential dilutive common stock equivalents (in shares)													143	105	184
Weighted average common shares outstanding - Diluted (in shares)													10,546	10,814	11,029
Net income per common share - Basic	$ 0.94	$ 0.91	$ 0.81	$ 0.81	$ 0.70	$ 0.54	$ 0.48	$ 0.49	$ 0.56	$ 0.55	$ 0.54	$ 0.53	$ 3.47	$ 2.21	$ 2.18
Net income per common share - Diluted	$ 0.93	$ 0.90	$ 0.80	$ 0.80	$ 0.69	$ 0.54	$ 0.47	$ 0.49	$ 0.55	$ 0.54	$ 0.53	$ 0.52	$ 3.43	$ 2.19	$ 2.14
Stock options and common stock excluded from the income per share calculation as their effect would have been anti-dilutive (in shares)													259	414	243