Earnings Per Share - Treasury stock method (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Earnings Per Share
Net income attributable to common shareholders	$ 7,104	$ 7,370	$ 21,888	$ 19,833
Weighted-average common shares outstanding for basic earnings per share	14,274	13,777	13,957	13,759
Basic earnings per common share	$ 0.49	$ 0.53	$ 1.53	$ 1.44
Dilutive effect of stock-based awards	352	294	360	301
Weighted-average common shares outstanding for diluted earnings per share	14,626	14,071	14,317	14,060
Diluted earnings per common share	$ 0.48	$ 0.52	$ 1.49	$ 1.41