Quarterly Consolidated Financial Information - Unaudited (Details) - USD ($) $ / shares in Units, shares in Thousands, $ 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
Total revenue	$ 118,190	$ 80,958	$ 78,702	$ 70,497	$ 63,189	$ 65,861	$ 67,844	$ 77,946	$ 348,347	$ 274,840	$ 207,274
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 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 earnings 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
Basic weighted average common shares outstanding (in shares)	5,782	5,900	5,878	6,104	6,090	6,055	6,036	6,114	5,915	6,074	6,570
Diluted weighted average common shares outstanding (in shares)	5,939	6,004	5,991	6,256	6,201	6,184	6,158	6,240	6,046	6,220	6,714
Revenue									$ 87,009	$ 80,189	$ 57,091
ASU 2014-09 | Adjustment
Revenue		$ 3,000	$ 4,400	$ 6,600