Unaudited Quarterly Financial Data (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								6 Months Ended	12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Jun. 30, 2016	Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2015	Dec. 31, 2014
Unaudited Quarterly Information
Total revenues	$ 261,692	$ 205,427	$ 188,096	$ 124,090	$ 225,720	$ 153,827	$ 79,389	$ 58,830		$ 779,305		$ 517,766	$ 285,913
Total expenses	244,196	193,492	180,800	123,231	209,380	148,307	83,855	63,838		741,719		505,380	287,516
Income (loss) before income taxes	17,496	11,935	7,296	859	16,340	5,520	(4,466)	(5,008)	$ 20,100	37,586	$ 30,000	12,386	(1,603)
Less: income tax expense (benefit)	438	38	(110,065)	68	436					109,521		(436)
Net income (loss)	$ 17,058	$ 11,897	$ 117,361	$ 791	$ 15,904	$ 5,520	$ (4,466)	$ (5,008)		$ 147,107		$ 11,950	$ (1,932)
Earnings (loss) per share:
Basic earnings (loss) per share (in dollars per share)	$ 0.77	$ 0.53	$ 5.24	$ 0.04	$ 0.72	$ 0.25	$ (0.20)	$ (0.23)		$ 6.58		$ 0.54	$ (0.09)
Diluted earnings (loss) per share (in dollars per share)	$ 0.68	$ 0.49	$ 4.45	$ 0.04	$ 0.65	$ 0.25	$ (0.20)	$ (0.23)		$ 5.66		$ 0.54	$ (0.09)