Acquisitions - 2015 Acquisitions (Details) - USD ($) $ in Thousands		3 Months Ended								7 Months Ended	12 Months Ended
	May 24, 2015	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, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Acquisitions
Cash paid for acquisitions of businesses											$ 51,664	$ 22,278	$ 128,245
Operating revenues		$ 708,277	$ 662,103	$ 631,355	$ 562,550	$ 538,948	$ 519,729	$ 571,591	$ 597,571		2,564,285	2,227,839	3,864,437
Assets:
Goodwill		173,226				166,917				$ 166,659	173,226	166,917	166,659
Liabilities:
Net income (loss)		$ (116,344)	$ (148,532)	$ (132,951)	$ (148,984)	$ (335,587)	$ (111,211)	$ (184,650)	$ (398,294)		$ (546,811)	$ (1,029,742)	(372,675)
Joint Venture in Saudi Arabia
Acquisitions
Cash paid for acquisitions of businesses	$ 106,000
Remaining equity interest acquired (as a percent)	49.00%
Ownership percentage	51.00%
Carrying value of equity method investment	$ 44,700
Excess of fair value over carrying value of long-lived assets													$ 2,300
Operating revenues										248,900
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	2 years
Assets:
Cash	$ 48,058
Accounts receivable	153,819
Other current assets	58,021
Property, plant and equipment, net	89,643
Intangible assets	28,784
Goodwill	75,634
Other long-term assets	7,709
Total assets	461,668
Liabilities:
Accounts payable	206,599
Accrued liabilities	74,393
Intangible liability	13,472
Deferred tax liability	4,823
Other long-term liabilities	9,400
Total liabilities	308,687
Net assets acquired	$ 152,981
Net income (loss)										$ 6,000