Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Earnings Per Share
Shares not included in computation of diluted weighted average earnings per common									400	700	0
Net income attributable to common shareholders	$ 17,274	$ 8,834	$ 7,528	$ 6,261	$ 41,864	$ 4,939	$ 5,657	$ 7,839	$ 39,898	$ 60,299	$ 13,780
Basic weighted average common shares outstanding (in shares)	5,782,000	5,900,000	5,878,000	6,104,000	6,090,000	6,055,000	6,036,000	6,114,000	5,915,000	6,074,000	6,570,000
Potentially dilutive common shares									131,000	146,000	144,000
Diluted weighted average common shares outstanding	5,939,000	6,004,000	5,991,000	6,256,000	6,201,000	6,184,000	6,158,000	6,240,000	6,046,000	6,220,000	6,714,000
Basic weighted average earnings per common share (in dollars per share)	$ 2.99	$ 1.50	$ 1.28	$ 1.03	$ 6.87	$ 0.82	$ 0.94	$ 1.28	$ 6.75	$ 9.93	$ 2.10
Diluted weighted average earnings per common share (in dollars per share)	$ 2.91	$ 1.47	$ 1.26	$ 1.00	$ 6.75	$ 0.80	$ 0.92	$ 1.25	$ 6.60	$ 9.69	$ 2.05