Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended												12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Quarterly Financial Data (Unaudited)
Net revenues	$ 23,952	$ 32,173	$ 35,180	$ 33,159	$ 39,407	$ 33,116	$ 35,031	$ 30,971	$ 36,236	$ 31,465	$ 32,618	$ 29,471	$ 124,464	$ 138,525	$ 129,790
Operating income (loss)	(604)	8,407	10,496	7,057	12,603	9,579	10,677	7,164	11,079	7,951	8,780	7,056	25,356	40,023	34,867
Net income (loss)	$ (22,044)	$ 682	$ 5,181	$ 2,745	$ 5,922	$ 4,349	$ 5,029	$ 2,700	$ 4,934	$ 2,910	$ 3,431	$ 2,462	$ (13,436)	$ 18,000	$ 13,739
Earnings (loss) per share:
Basic (in dollars per share)	$ (0.56)	$ 0.02	$ 0.13	$ 0.07	$ 0.15	$ 0.11	$ 0.12	$ 0.06	$ 0.11	$ 0.07	$ 0.08	$ 0.06	$ (0.33)	$ 0.43	$ 0.32
Dilutive (in dollars per share)	$ (0.56)	$ 0.02	$ 0.13	$ 0.07	$ 0.15	$ 0.11	$ 0.12	$ 0.06	$ 0.11	$ 0.07	$ 0.08	$ 0.06	$ (0.33)	$ 0.43	$ 0.31