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Revenue - Narrative (Details)
6 Months Ended
Jun. 30, 2018
USD ($)
Revenue from Contract with Customer [Abstract]  
Percentage of revenues derived from services provided 90.00%
Percentage of revenues derived from other sources 10.00%
Remaining performance obligations $ 268,800,000
Remaining performance obligation expected to be recognized in next 12 months, percentage 0.95
Disaggregation of Revenue [Line Items]  
Revenue recognized related to contract liabilities 16,300,000
Contract costs 1,200,000
Recognized contract costs $ 4,100,000
Minimum  
Disaggregation of Revenue [Line Items]  
Bill and collection period 60 days
Maximum  
Disaggregation of Revenue [Line Items]  
Bill and collection period 120 days