Annual report pursuant to Section 13 and 15(d)

Revenue from Contracts with Customers - Narrative (Details)

v3.19.1
Revenue from Contracts with Customers - Narrative (Details)
$ in Thousands
 3 Months Ended 9 Months Ended 12 Months Ended
Dec. 31, 2018
USD ($)
Sep. 30, 2018
USD ($)
Jun. 30, 2018
USD ($)
Mar. 31, 2018
USD ($)
Dec. 31, 2017
USD ($)
Sep. 30, 2017
USD ($)
Jun. 30, 2017
USD ($)
Mar. 31, 2017
USD ($)
Sep. 30, 2018
business_line
Dec. 31, 2018
USD ($)
business_line
Dec. 31, 2017
USD ($)
Dec. 31, 2016
USD ($)
Revenue from Contract with Customer [Abstract]                        
Number of business lines | business_line                 2 2    
Disaggregation of Revenue [Line Items]                        
Typical payment term (in days)                   30 days    
Revenues $ 129,148 $ 123,395 $ 118,603 $ 109,675 $ 116,334 $ 118,308 $ 109,607 $ 98,271   $ 480,821 $ 442,520 $ 427,004
Capitalized mobilization costs $ 5,300       $ 3,100         5,300 3,100  
Amortization of capitalized mobilization cost                   $ 6,700 1,200  
Minimum                        
Disaggregation of Revenue [Line Items]                        
Revenue, remaining performance obligation, expected timing of satisfaction, period                   2    
Maximum                        
Disaggregation of Revenue [Line Items]                        
Revenue, remaining performance obligation, expected timing of satisfaction, period                   60    
Reimbursable revenue                        
Disaggregation of Revenue [Line Items]                        
Revenues                   $ 54,600 $ 57,800 $ 69,300