Other Financial Statement Disclosures (Narrative) (Details) - USD ($)	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Supplemental Cash Flow Information
Accrued capital expenditures	$ 27,000,000	$ 57,100,000
Interest capitalized in connection with rig construction projects	$ 0	$ 7,500,000
Income Taxes
Effective tax rate	3.20%	12.20%