Other Financial Statement Disclosures (Narrative) (Details) $ in Millions		1 Months Ended	3 Months Ended		6 Months Ended
	Jul. 31, 2015 rig	Feb. 28, 2014 USD ($)	Jun. 30, 2015 USD ($)	Jun. 30, 2014 USD ($)	Dec. 31, 2015 USD ($)	Jun. 30, 2015 USD ($)	Jun. 30, 2014 USD ($)
Supplemental Cash Flow Information
Accrued capital expenditures						$ 41.4	$ 46.6
Interest capitalized in connection with rig construction projects			$ 8.7	$ 13.0		$ 16.2	$ 30.5
Income Taxes
Effective tax rate			8.30%	5.70%		10.70%	2.50%
Litigation Settlement
Proceeds from litigation settlements							$ 20.9
Subsequent Event [Member]
Income Taxes
Number of jack-up rigs sold | rig	2
Subsequent Event [Member] | Forecast [Member] | Minimum [Member]
Income Taxes
Increase in valuation allowance					$ 6.0
Subsequent Event [Member] | Forecast [Member] | Maximum [Member]
Income Taxes
Increase in valuation allowance					$ 9.0
Rowan land rig [Member]
Discontinued Operations
Net assets of discontinued operations		$ 4.1
Assets of discontinued operations		24.2
Deferred revenues classified as liabilities of discontinued operations		20.1
Proceeds from sale of rig		$ 6.0
Gain (loss) on disposals of property and equipment							$ 4.0