Segment Information - Eliminations Footnote (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Operating income (loss)
Operating income (loss)	$ 323,397	$ 334,566
Gross profit	463,416	472,154
Assets elimination
Accounts receivable	987,655		$ 868,837
Other	26,606		27,684
Total assets	6,972,813		$ 6,855,732
Eliminations
Operating income (loss)
Operating income (loss)	(265)	(1,571)
Gross profit		$ (1,600)
Assets elimination
Accounts receivable	(72,400)
Elimination of intra-company debt	(12,900)
Other	(12,300)
Total assets	$ (97,631)