Earnings Per Share - Treasury stock method (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	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, 2019	Dec. 31, 2018	Dec. 31, 2017
Earnings Per Share
Net income attributable to common shareholders	$ 7,652	$ 7,104	$ 8,348	$ 6,436	$ 6,033	$ 7,370	$ 5,599	$ 6,864	$ 29,540	$ 25,866	$ 15,001
Weighted-average common shares outstanding for basic earnings per share									14,736	13,763	13,653
Basic earnings per common share	$ 0.44	$ 0.49	$ 0.60	$ 0.47	$ 0.44	$ 0.53	$ 0.41	$ 0.50	$ 1.96	$ 1.88	$ 1.10
Dilutive effect of stock-based awards									357	300	354
Weighted-average common shares outstanding for diluted earnings per share									15,093	14,063	14,007
Diluted earnings per common share	$ 0.43	$ 0.48	$ 0.59	$ 0.46	$ 0.43	$ 0.52	$ 0.40	$ 0.49	$ 1.91	$ 1.84	$ 1.07