Supplemental Balance Sheet, Income Statement and Cash Flow Information - Reclass Accumulated Other (Details) - USD ($) $ 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
Unrealized (gains) losses on available-for-sale securities that were reclassified from net income
Investment income (loss)									$ 1,194	$ 1,183	$ 2,308
Impairments and other charges									44,536	498,499	368,967
Interest expense									222,889	185,360	181,928
General and administrative expenses									251,184	227,639	324,328
Other expense (income), net									14,880	44,174	(39,172)
Income (loss) from continuing operations before income taxes									(580,084)	(1,198,075)	(427,535)
Tax expense (benefit)									82,970	186,831	98,038
Net income (loss)	$ (115,167)	$ (146,419)	$ (130,980)	$ (148,067)	$ (334,462)	$ (110,026)	$ (187,549)	$ (397,570)	(540,633)	(1,029,607)	(372,294)
Reclassification adjustment for (gains)/losses included in net income (loss)
Unrealized (gains) losses on available-for-sale securities that were reclassified from net income
Impairments and other charges									970	3,495
Interest expense									613	613	613
General and administrative expenses									200	1,061	1,104
Other expense (income), net										3,059	5,365
Income (loss) from continuing operations before income taxes									(1,783)	(8,228)	(7,082)
Tax expense (benefit)									315	1,551	648
Net income (loss)									$ (1,468)	$ (6,677)	$ (6,434)