Quarterly report pursuant to Section 13 or 15(d)

Revenue from Contracts with Customers - Narrative (Details)

v3.8.0.1
Revenue from Contracts with Customers - Narrative (Details) - USD ($)
 3 Months Ended
Mar. 31, 2018
Jan. 01, 2018
Dec. 31, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]      
Increase (decrease) in retained earnings $ 238,378,000 $ 231,390,000 $ 235,844,000
Contract with customer, liability, noncurrent 7,038,000    
Contract with customer, asset, reclassified to receivable 120,072,000    
Contract with customer, asset, revenue recognized 87,440,000    
Contract with customer, liability, revenue recognized 17,843,000    
Contract with customer, liability, billings 17,000,000    
Revenue, remaining performance obligation $ 1,380,000,000    
Revenue, remaining performance obligation, percentage 30.00%    
Capitalized commission costs   927,000  
Capitalized contract cost, impairment loss $ 0    
Capitalized contract cost, project development costs $ 2,440,000    
Minimum      
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]      
Contract receivable retainage percentage 5.00%    
Maximum      
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]      
Contract receivable retainage percentage 10.00%    
Effect of Change Higher/(Lower) | Accounting Standards Update 2014-09      
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]      
Increase (decrease) in retained earnings $ (3,345,000) $ (4,454,000)