Selected 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, 2017	Dec. 31, 2016	Dec. 31, 2015
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 148,775	$ 144,671	$ 155,199	$ 156,174	$ 154,174	$ 156,017	$ 160,258	$ 163,524	$ 604,819	$ 633,973	$ 681,100
Gross Profit	77,192	80,104	91,849	92,501	90,935	91,684	97,375	99,424	341,646	379,418	399,006
Net (loss) income	$ 85,536	$ (451,718)	$ 21,280	$ 14,363	$ 21,347	$ 24,273	$ 26,829	$ 25,543	$ (330,539)	$ 97,992	$ 104,923
Basic (USD per share)	$ 4.68	$ (24.98)	$ 1.18	$ 0.80	$ 1.18	$ 1.33	$ 1.46	$ 1.38	$ (18.28)	$ 5.36	$ 5.55
Diluted (USD per share)	$ 4.67	$ (24.98)	$ 1.18	$ 0.79	$ 1.18	$ 1.33	$ 1.45	$ 1.37	$ (18.28)	$ 5.33	$ 5.52
Impairment of goodwill and intangible assets		$ 531,600							$ 531,634	$ 0	$ 0