Summary of Significant Accounting Policies - Calculation Of Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended												12 Months Ended
	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, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accounting Standards Update and Change in Accounting Principle [Abstract]
Net income	$ 10,100	$ 11,855	$ 9,900	$ 1,033	$ 4,580	$ 7,538	$ 4,261	$ 4,312	$ 4,848	$ 5,264	$ 5,830	$ 4,062	$ 32,888	$ 20,691	$ 20,004
Basic weighted average common shares outstanding (in shares)													6,354,687	6,708,622	6,877,573
Dilutive effect of potential common shares from awards granted under equity incentive program (in shares)													76,000	99,000	104,000
Total (in shares)													6,431,367	6,808,209	6,981,557
Earnings per common share
Basic (in USD per share)	$ 1.62	$ 1.87	$ 1.54	$ 0.16	$ 0.70	$ 1.13	$ 0.62	$ 0.63	$ 0.70	$ 0.77	$ 0.85	$ 0.59	$ 5.18	$ 3.08	$ 2.91
Diluted (in USD per share)	$ 1.59	$ 1.84	$ 1.52	$ 0.16	$ 0.69	$ 1.11	$ 0.62	$ 0.62	$ 0.69	$ 0.75	$ 0.84	$ 0.58	$ 5.11	$ 3.04	$ 2.86