Annual report pursuant to Section 13 and 15(d)

Contract Revenue and Percentage-of-Completion Method - Revenues from Major Customers (Details)

v3.6.0.2
Contract Revenue and Percentage-of-Completion Method - Revenues from Major Customers (Details) - USD ($)
$ in Thousands
 3 Months Ended 12 Months Ended
Dec. 31, 2016
Sep. 30, 2016
Jun. 30, 2016
Mar. 31, 2016
Dec. 31, 2015
Sep. 30, 2015
Jun. 30, 2015
Mar. 31, 2015
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Revenue, Major Customer [Line Items]                      
Revenue $ 55,461 $ 65,384 $ 81,502 $ 83,979 $ 55,018 $ 67,531 $ 84,338 $ 99,233 $ 286,326 $ 306,120 $ 506,639
Customer A                      
Revenue, Major Customer [Line Items]                      
Revenue                 $ 65,981    
Customer B                      
Revenue, Major Customer [Line Items]                      
Revenue                   55,775 160,173
Customer C                      
Revenue, Major Customer [Line Items]                      
Revenue                   $ 36,320  
Customer D                      
Revenue, Major Customer [Line Items]                      
Revenue                     $ 98,644