Segment Information - Eliminations Footnote (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
Operating income (loss)
Operating income (loss)	$ 195,947	$ 271,015	$ 265,353	$ 334,566	$ 56,024	$ 283,855	$ 256,122	$ 131,965	$ 1,066,881	$ 727,966	$ (72,784)
Gross profit	320,824	$ 396,518	$ 392,518	$ 472,154	309,942	$ 408,503	$ 380,383	$ 236,036	1,582,014	1,334,864	731,718
Asset impairment charges										132,839	428,500
Assets elimination
Accounts receivable	868,837				729,784				868,837	729,784
Other	27,684				29,514				27,684	29,514
Total assets	6,855,732				6,423,732				6,855,732	6,423,732
Eliminations
Operating income (loss)
Operating income (loss)									689	(9,250)	$ 4,974
Gross profit										(11,100)
Asset impairment charges										1,800
Assets elimination
Accounts receivable	(106,100)				(112,300)				(106,100)	(112,300)
Elimination of intra-company debt	(13,400)				(12,100)				(13,400)	(12,100)
Other	(12,000)				12,600				(12,000)	12,600
Total assets	$ (131,496)				$ (137,012)				$ (131,496)	$ (137,012)