Annual report pursuant to Section 13 and 15(d)

Summary of Significant Accounting Policies - Additional Information (Detail)

v3.8.0.1
Summary of Significant Accounting Policies - Additional Information (Detail)
$ in Millions
 12 Months Ended
Dec. 31, 2017
USD ($)
country
segment
business_line
ft
Dec. 31, 2016
USD ($)
Dec. 31, 2015
USD ($)
Revenue, Major Customer [Line Items]      
Number of business lines | business_line 2    
Number of reportable segments | segment 2    
Number of countries entity has operated in since inception (more than) | country 50    
Number of countries with operations | country 19    
Percentage accounted for under the equity method 50.00%    
Reimbursement cost $ 57.8 $ 69.3 $ 87.8
Capitalized interest costs of construction of rigs $ 0.0 0.2 0.2
Consumed and replenished period 1 year    
Deposits in domestic bank $ 97.6 81.4  
Deposits in foreign banks 45.6 39.7  
Exxon Neftegas Limited (ENL)      
Revenue, Major Customer [Line Items]      
Reimbursement revenue $ 50.8 $ 67.0 $ 75.8
Customer Concentration Risk | Sales Revenue, Net | Exxon Neftegas Limited (ENL)      
Revenue, Major Customer [Line Items]      
Percentage of revenue from major customer 31.30% 38.70% 27.90%
Customer Concentration Risk | Sales Revenue, Net | BP Exploration Alaska, Inc. (BP)      
Revenue, Major Customer [Line Items]      
Percentage of revenue from major customer 9.70%    
International & Alaska Drilling      
Revenue, Major Customer [Line Items]      
Contract term 1 year    
International & Alaska Drilling | Customer Concentration Risk | Sales Revenue, Net | Exxon Neftegas Limited (ENL)      
Revenue, Major Customer [Line Items]      
Percentage of revenue from major customer 55.90% 57.50% 45.60%
International & Alaska Drilling | Customer Concentration Risk | Sales Revenue, Net | BP Exploration Alaska, Inc. (BP)      
Revenue, Major Customer [Line Items]      
Percentage of revenue from major customer 17.40%    
Minimum      
Revenue, Major Customer [Line Items]      
Estimated Useful Life (Years) 3 years    
Minimum | U.S. (Lower 48) Drilling      
Revenue, Major Customer [Line Items]      
Underwater drilling depth (in feet) | ft 6    
Contract term 20 days    
Maximum      
Revenue, Major Customer [Line Items]      
Estimated Useful Life (Years) 6 years    
Maximum | U.S. (Lower 48) Drilling      
Revenue, Major Customer [Line Items]      
Underwater drilling depth (in feet) | ft 12    
Contract term 180 days