Commitments and Contingencies - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012 Contract	Dec. 31, 2011	Dec. 31, 2010
Schedule Of Commitments And Contingencies [Line Items]
Deductible for marine liability coverage including personal injury claims, per first occurrence	$ 10,000,000
Range of deductible for liability coverage for personal injury claims, lower limit	5,000,000
Range of deductible for liability coverage for personal injury claims, upper limit	100,000,000
Estimated liability for personal injury claims	36,100,000	32,700,000
Reserve for personal injury claims recorded in accrued liabilities	9,900,000	10,100,000
Reserve for personal injury claims recorded in other liabilities	26,200,000	22,600,000
Number of turnkey contracts for drillship construction	4
Total unconditional purchase obligation for drillships	2,600,000,000
Other Purchase obligations	0	0
Rental expense under operating leases	10,800,000	9,300,000	8,000,000
Future minimum rental payments under leases, in current years	2,500,000
Future minimum rental payments under leases, in two years	1,600,000
Future minimum rental payments under leases , in years three through five following reporting period	200,000
Future minimum rental payments under leases, thereafter	0
Contingent liability under letters of credit and other bonds	126,500,000
Collateral deposits related to agreements	111,500,000
Hyundai Heavy Industries Co Ltd [Member]
Schedule Of Commitments And Contingencies [Line Items]
Total number of installments due under each drillship turnkey construction agreement	2
First Installments on Drillships aggregate amount	169,300,000	478,300,000
Keppel AmFELSLLC [Member]
Schedule Of Commitments And Contingencies [Line Items]
Total unconditional purchase obligation	310,000,000
Number of installments due under each rig construction agreement	11
Milestone payment		14,600,000
Number of installments paid	5
Vessel modification agreement Payment during the period	65,700,000
Moored Semi Submersible Rig [Member]
Schedule Of Commitments And Contingencies [Line Items]
Total water depth in feet for new moored semisubmersible rig	6,000
Jurong Shipyard Pte Ltd [Member]
Schedule Of Commitments And Contingencies [Line Items]
Total unconditional purchase obligation	370,000,000
Number of installments due under each rig construction agreement	12
Number of installments paid	2
Vessel modification agreement Payment during the period	$ 27,000,000