Commitments and Contingencies - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2013 Installment	Dec. 31, 2012
Schedule Of Commitments And Contingencies [Line Items]
Deductible for marine liability coverage including personal injury claims, per first occurrence	$ 10.0
Range of deductible for liability coverage for personal injury claims, lower limit	5.0
Range of deductible for liability coverage for personal injury claims, upper limit	100.0
Other purchase obligations	0	0
Contingent liability under letters of credit and other bonds	70.2
Collateral deposits related to agreements	58.2
Personal Injury Claims [Member]
Schedule Of Commitments And Contingencies [Line Items]
Personal injury claims recorded	35.5	36.1
Personal Injury Claims [Member] | Accrued Liabilities [Member]
Schedule Of Commitments And Contingencies [Line Items]
Personal injury claims recorded	8.1	9.9
Personal Injury Claims [Member] | Other Liabilities [Member]
Schedule Of Commitments And Contingencies [Line Items]
Personal injury claims recorded	27.4	26.2
Keppel AmFELS LLC [Member]
Schedule Of Commitments And Contingencies [Line Items]
Cost of enhancement of project	335.0
Expected amount of second installments payable in next 12 months	21.9
Number of installments due under each rig construction agreement	11
Number of installments paid	9
Vessel modification agreement Payment during the period	58.4	65.7
Hyundai Heavy Industries Co Ltd [Member] | UltraDeepwater Floater Rig [Member]
Schedule Of Commitments And Contingencies [Line Items]
Water depth of rig	10,000
Cost of enhancement of project	755.0
Total number of installments due under each turnkey construction agreements	2
Cost of construction per shipyard agreement	628.5
First installment for Ultra-Deep water Floater Construction	188.6
Final installment for Ultra-Deep water Floater Construction	439.9
Hyundai Heavy Industries Co Ltd [Member] | Ultra-deepwater drillships [Member]
Schedule Of Commitments And Contingencies [Line Items]
Cost of enhancement of project	2,600.0
Total number of installments due under each turnkey construction agreements	2
Number of turnkey contracts for drill ship construction	4
First Installments on Drill ships aggregate amount for Drill ship Construction	647.6
Hyundai Heavy Industries Co Ltd [Member] | Ultra-deepwater drillships [Member] | First Quarter 2014 [Member]
Schedule Of Commitments And Contingencies [Line Items]
Expected amount of second installments payable in next 12 months	394.0
Hyundai Heavy Industries Co Ltd [Member] | Ultra-deepwater drillships [Member] | Fourth Quarter of 2013 [Member]
Schedule Of Commitments And Contingencies [Line Items]
Expected amount of second installments payable in next 12 months	394.0
Hyundai Heavy Industries Co Ltd [Member] | Ultra-deepwater drillships [Member] | Second Quarter of 2014 [Member]
Schedule Of Commitments And Contingencies [Line Items]
Expected amount of second installments payable in next 12 months	395.0
Hyundai Heavy Industries Co Ltd [Member] | Ultra-deepwater drillships [Member] | Fourth Quarter of 2014 [Member]
Schedule Of Commitments And Contingencies [Line Items]
Expected amount of second installments payable in second year	395
Jurong Shipyard Pte Ltd [Member]
Schedule Of Commitments And Contingencies [Line Items]
Cost of enhancement of project	370.0
Number of installments due under each rig construction agreement	12
Number of installments paid	5
Vessel modification agreement Payment during the period	33.8	27.0
Construction agreement balance amount payable	74.3
Keppel FELS Limited [Member]
Schedule Of Commitments And Contingencies [Line Items]
Cost of enhancement of project	120.0
Cost of construction per shipyard agreement	29.0
Number of installments due under each rig construction agreement	7
Number of installments paid	2
Vessel modification agreement Payment during the period	10.1
Construction agreement balance amount payable	$ 18.8