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Revenues - Additional Information (Details) - USD ($)
$ in Thousands
3 Months Ended 6 Months Ended
Jun. 30, 2018
Jun. 30, 2017
Jun. 30, 2018
Jun. 30, 2017
Jan. 01, 2018
Dec. 31, 2017
Dec. 31, 2016
Disaggregation of Revenue [Line Items]              
Cumulative effect of new accounting principle in period of adoption           $ 268  
Contract with customer, liability, current $ 43,088   $ 43,088     51,597 $ 62,700
Difference Between Work Performed On Open Contracts And Contractual Billing Terms              
Disaggregation of Revenue [Line Items]              
Changes in contract assets (liabilities)     (2,000)        
Difference Related To Customer Advances On Certain Contract              
Disaggregation of Revenue [Line Items]              
Changes in contract assets (liabilities)     $ 8,500        
Products and Services              
Disaggregation of Revenue [Line Items]              
Revenue recognized, percent 93.40% 93.90% 94.20% 93.40%      
Product              
Disaggregation of Revenue [Line Items]              
Revenue recognized, percent 6.60% 6.10% 5.80% 6.60%      
Retained Earnings              
Disaggregation of Revenue [Line Items]              
Cumulative effect of new accounting principle in period of adoption           $ 268  
Accounting Standards Update 2014-09 | Retained Earnings              
Disaggregation of Revenue [Line Items]              
Cumulative effect of new accounting principle in period of adoption         $ 300    
Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09              
Disaggregation of Revenue [Line Items]              
Changes in revenues     $ (300)