Acquisitions and Dispositions Acquisitions and Dispositions (Details 2) - USD ($)	12 Months Ended
	Dec. 31, 2017	Mar. 02, 2018	Feb. 13, 2018	Dec. 31, 2016	Dec. 31, 2015
Business Acquisition [Line Items]
Purchase price	$ 40,000,000
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares	7,772,021
Disposal Group, Including Discontinued Operation, Consideration	$ 3,100,000.000000000
Notes Receivable, Related Parties	7,500,000
Loans Receivable with Fixed Rates of Interest	0.015
Asset Retirement Obligation	58,402,000			$ 55,478,000	$ 57,449,000
Line of Credit Facility, Maximum Borrowing Capacity	200,000,000
Discontinued Operation, Gain (Loss) on Disposal of Discontinued Operation, Net of Tax	33,000,000
discontinued operation, loss net of tax, maximum	35,000,000
Maritech [Member]
Business Acquisition [Line Items]
Asset Retirement Obligation	$ 46,800,000
Subsequent Event [Member]
Business Acquisition [Line Items]
Contingent consideration, maximum			$ 15,000,000
Line of Credit Facility, Maximum Borrowing Capacity		$ 47,000,000