Annual report pursuant to Section 13 and 15(d)

Segments - Narrative (Details)

v3.8.0.1
Segments - Narrative (Details)
3 Months Ended 12 Months Ended
Dec. 31, 2017
USD ($)
Sep. 30, 2017
USD ($)
Jun. 30, 2017
USD ($)
Mar. 31, 2017
USD ($)
Dec. 31, 2016
USD ($)
Sep. 30, 2016
USD ($)
Jun. 30, 2016
USD ($)
Mar. 31, 2016
USD ($)
Dec. 31, 2017
USD ($)
Segment
Dec. 31, 2016
USD ($)
Dec. 31, 2015
USD ($)
Segment Reporting Information [Line Items]                      
Number of reportable segments | Segment                 2    
Revenues $ 193,699,000 $ 263,495,000 $ 314,213,000 $ 296,096,000 $ 275,489,000 $ 298,035,000 $ 357,100,000 $ 291,037,000 $ 1,067,503,000 $ 1,221,661,000 $ 491,738,000
Intersegment Elimination                      
Segment Reporting Information [Line Items]                      
Revenues                 0    
Inter-segment allocation of interest expense                 $ 0    
Customer 1 | Customer Concentration Risk | Sales Revenue, Net                      
Segment Reporting Information [Line Items]                      
Concentration risk percentage                 10.00%   13.00%
Customer 1 | Customer Concentration Risk | Accounts Receivable                      
Segment Reporting Information [Line Items]                      
Concentration risk percentage                   10.00%  
Customer 2 | Customer Concentration Risk | Sales Revenue, Net                      
Segment Reporting Information [Line Items]                      
Concentration risk percentage                 10.00%