Other Financial Statement Disclosures - Narrative (Details) $ in Millions		3 Months Ended		9 Months Ended		12 Months Ended
	Jan. 05, 2018 USD ($) drilling_unit	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)
Supplemental Cash Flow Information [Line Items]
Number of Rigs Purchased at Auction | drilling_unit	2
Tax Cuts and Jobs Act of 2017, Incomplete Accounting, Transition Tax for Accumulated Foreign Earnings, Provisional Income Tax Expense				$ 26.4		$ 34.1
Tax Cuts and Jobs Act of 2017, Incomplete Accounting, Change in Tax Rate, Provisional Income Tax Expense (Benefit)				61.6		56.7
Supplemental Cash Flow Information
Accrued capital expenditures				$ 26.5	$ 12.4
Income Taxes
Effective tax rate		(2.50%)	51.00%	(1.80%)	(293.70%)
Provision (benefit) for income taxes		$ 3.5	$ (21.8)	$ 5.8	$ 29.3
Increase (decrease) in income tax expense as compared to prior year periods		$ 25.3		(23.5)
P-59 [Member]
Supplemental Cash Flow Information [Line Items]
Purchase Price of Rigs Won at Auction	38.5
P-60 [Member]
Supplemental Cash Flow Information [Line Items]
Purchase Price of Rigs Won at Auction	38.5
P-59 and P60 Rigs [Member]
Supplemental Cash Flow Information [Line Items]
Purchase Price of Rigs Won at Auction	77.0
Security Deposit						7.7
Purchase Price of Rigs Won at Auction less Deposit	69.3
Transaction Costs	$ 1.5
Foreign Tax Authority [Member]
Supplemental Cash Flow Information [Line Items]
Tax Cuts and Jobs Act of 2017, Incomplete Accounting, Change in Tax Rate, Provisional Income Tax Expense (Benefit)				$ 33.7		$ 38.3