Annual report pursuant to Section 13 and 15(d)

CONTRACT REVENUE AND PERCENTAGE-OF-COMPLETION METHOD - Revenues from Major Customers (Details)

v3.8.0.1
CONTRACT REVENUE AND PERCENTAGE-OF-COMPLETION METHOD - Revenues from Major Customers (Details) - USD ($)
$ in Thousands
 3 Months Ended 12 Months Ended
Dec. 31, 2017
Sep. 30, 2017
Jun. 30, 2017
Mar. 31, 2017
Dec. 31, 2016
Sep. 30, 2016
Jun. 30, 2016
Mar. 31, 2016
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Revenue, Major Customer [Line Items]                      
Revenue $ 37,277 $ 49,884 $ 45,868 $ 37,993 $ 55,461 $ 65,384 $ 81,502 $ 83,979 $ 171,022 $ 286,326 $ 306,120
Customer A                      
Revenue, Major Customer [Line Items]                      
Revenue                 44,724    
Customer B                      
Revenue, Major Customer [Line Items]                      
Revenue                 $ 21,781    
Customer C                      
Revenue, Major Customer [Line Items]                      
Revenue                   $ 65,981  
Customer D                      
Revenue, Major Customer [Line Items]                      
Revenue                     55,775
Customer E                      
Revenue, Major Customer [Line Items]                      
Revenue                     $ 36,320