Fixed Assets and Asset Retirement Obligations (Narrative) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Asset Retirement Obligations Details [Line Items]
Depreciation expense	$ 226,000,000	$ 194,000,000	$ 124,200,000
Depletion	1,500,000	0	0
Gain on sales of assets	40,311,000	0	0
Asset retirement obligation	198,187,000	213,726,000	$ 188,662,000
Accrued Liabilities [Member]
Asset Retirement Obligations Details [Line Items]
Asset retirement obligation	$ 20,900,000	$ 22,400,000