Debt Credit Agreement (Details) - USD ($)	Apr. 30, 2019	Mar. 31, 2019	Dec. 19, 2018
Revolving Credit Facility | Third Amended Credit Agreement
Debt Instrument [Line Items]
Maximum borrowing commitment		$ 500,000,000
Maximum facility amount		$ 1,500,000,000
Line of Credit | San Mateo Credit Facility
Debt Instrument [Line Items]
Maximum borrowing commitment			$ 250,000,000
Line of credit, accordian feature			$ 400,000,000
Subsequent Event | Revolving Credit Facility | Third Amended Credit Agreement
Debt Instrument [Line Items]
Increase in borrowing base	$ 900,000,000