Annual report pursuant to Section 13 and 15(d)

Reportable Segments - Narrative (Detail)

v3.8.0.1
Reportable Segments - Narrative (Detail)
$ in Thousands
 12 Months Ended
Dec. 31, 2017
USD ($)
segment
business_line
ft
Dec. 31, 2016
USD ($)
Dec. 31, 2015
USD ($)
Segment Reporting Information [Line Items]      
Number of business lines | business_line 2    
Number of reportable segments | segment 2    
Number of operating segments | segment 4    
Depreciation and amortization $ 122,373 $ 139,795 $ 156,194
Corporate      
Segment Reporting Information [Line Items]      
Depreciation and amortization $ 8,700 8,300 7,500
International & Alaska Drilling      
Segment Reporting Information [Line Items]      
Contract term 1 year    
Exxon Neftegas Limited (ENL)      
Segment Reporting Information [Line Items]      
Reimbursement revenue $ 50,800 $ 67,000 $ 75,800
Exxon Neftegas Limited (ENL) | Customer Concentration Risk | Sales Revenue, Net      
Segment Reporting Information [Line Items]      
Percentage of revenue from major customer 31.30% 38.70% 27.90%
Exxon Neftegas Limited (ENL) | Customer Concentration Risk | Sales Revenue, Net | International & Alaska Drilling      
Segment Reporting Information [Line Items]      
Percentage of revenue from major customer 55.90% 57.50% 45.60%
Exxon Neftegas Limited (ENL) | Customer Concentration Risk | Sales Revenue, Net of Reimbursable Revenues      
Segment Reporting Information [Line Items]      
Percentage of revenue from major customer 22.70% 27.50% 19.70%
Exxon Neftegas Limited (ENL) | Customer Concentration Risk | Sales Revenue, Net of Reimbursable Revenues | International & Alaska Drilling      
Segment Reporting Information [Line Items]      
Percentage of revenue from major customer 46.10% 45.00% 35.30%
BP Exploration Alaska, Inc. (BP) | Customer Concentration Risk | Sales Revenue, Net      
Segment Reporting Information [Line Items]      
Percentage of revenue from major customer 9.70%    
BP Exploration Alaska, Inc. (BP) | Customer Concentration Risk | Sales Revenue, Net | International & Alaska Drilling      
Segment Reporting Information [Line Items]      
Percentage of revenue from major customer 17.40%    
Minimum | U.S. (Lower 48) Drilling      
Segment Reporting Information [Line Items]      
Underwater drilling depth (in feet) | ft 6    
Contract term 20 days    
Maximum | U.S. (Lower 48) Drilling      
Segment Reporting Information [Line Items]      
Underwater drilling depth (in feet) | ft 12    
Contract term 180 days