Supplemental Schedule of Cash Flow Information - Non-Cash Financing and Investing Activity (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017
Supplemental Cash Flow Elements [Abstract]
Capital leases and notes issued for equipment	$ 3,321	$ 22,374
Asset retirement obligation additions (retirements)	(58)	0
Change in accrued property and equipment	$ 2,518	$ 0

Future cash outflow to pay for purchases of fixed assets that have occurred.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=6367179&loc=d3e4332-108586

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=6367179&loc=d3e4313-108586

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=6367179&loc=d3e4304-108586

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration