Commitments and Contingencies - Saudi Aramco (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) item
Additional contribution amount	$ 204.0
Saudi Aramco
Contribution	20.0
Joint Venture in Saudi Arabia
Additional contribution amount	$ 204.0
Number of additional drilling units and related assets contributed | item	5
Number of drilling units to backstop entity share to purchase in the event of insufficient cash | item	25