Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Income taxes disclosures
U.S. federal statutory rate (as a percent)			21.00%		35.00%
Income tax benefit related to the alternative minimum tax credits	$ 1,600
Tax benefit due to intangible asset impairment charge	25,300
Asset impairment charges	252,343	$ 675	$ 252,343	$ 1,138
Loss before income taxes	(265,659)	(34,158)	(281,716)	(43,045)
Income tax benefit	(28,025)	(13,341)	(28,255)	(23,868)
Domestic
Income taxes disclosures
Income tax benefit	(1,300)	(15,600)	(1,200)	(19,900)
Foreign
Income taxes disclosures
Income tax benefit	$ (26,700)	$ 2,300	$ (27,100)	$ (4,000)