Revenue from Contracts with Customers - Contract Liabilities Table (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2018		Sep. 30, 2018	Dec. 31, 2017
Change in Contracts with Customer, Liability [Roll Forward]
Balance at December 31, 2017		$ 0
Cumulative effect of adopting Topic 606		120,717
Cash received or receivable, excluding revenues recognized during the period	$ (3,700)	37,340	[1]
Revenues recognized during the period that were included in the adoption effect	(8,800)	(10,850)	[2]
Balance at September 30, 2018	147,207	147,207
Contract liabilities at September 30, 2018
Accrued liabilities				$ 8,031	$ 0
Other liabilities				139,176
Total contract liabilities from contracts with customers	$ 147,207	0		$ 147,207	$ 0
Change in Contract with Customer, Asset and Liability [Abstract]
Performance obligation satisfied in previous period		$ (7,500)

[1] Includes $(3.7) million for the three months ended September 30, 2018.

[2] Includes $(8.8) million for the three months ended September 30, 2018, of which $(7.5) million was from a performance obligation satisfied in a previous period related to the arbitration against SWEPI LP (see Note 11).