Selected Quarterly Financial Data (Unaudited) (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
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 214,198	$ 194,099	$ 184,471	$ 188,163	$ 176,708	$ 174,903	$ 188,654	$ 191,461	$ 780,931	$ 731,725	$ 787,566
Gross Profit	98,371	92,626	78,590	83,500	69,336	82,086	93,004	94,285	353,087	338,711	384,147
Net income (loss)	$ 26,981	$ 23,587	$ 12,713	$ 17,073	$ 69,900	$ (450,352)	$ 22,107	$ 15,595	$ 80,354	$ (342,750)	$ 101,002
Basic (USD per share)	$ 1.49	$ 1.31	$ 0.70	$ 0.93	$ 3.82	$ (24.91)	$ 1.23	$ 0.87	$ 4.43	$ (18.96)	$ 5.52
Diluted (USD per share)	$ 1.47	$ 1.29	$ 0.69	$ 0.92	$ 3.82	$ (24.91)	$ 1.23	$ 0.86	$ 4.37	$ (18.96)	$ 5.49
Impairment of goodwill and intangible assets						$ 531,600			$ 0	$ 531,634	$ 0