Debt Credit Agreement (Details) - Revolving Credit Facility - Third Amended Credit Agreement - USD ($)	1 Months Ended
	Oct. 31, 2018	Sep. 30, 2018	Mar. 31, 2018
Debt Instrument [Line Items]
Increase in borrowing base			$ 725,000,000
Maximum borrowing commitment		$ 400,000,000
Maximum facility amount		$ 500,000,000
Subsequent Event
Debt Instrument [Line Items]
Increase in borrowing base	$ 850,000,000.0
Maximum borrowing commitment	500,000,000.0
Increase in maximum credit facility	$ 1,500,000,000.0
Annual reduction in borrowing rate	0.25%