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Revenue - Narrative (Details) $ in Thousands	3 Months Ended
Revenue - Narrative (Details) $ in Thousands	Mar. 31, 2018 USD ($)
Contract With Customer, Asset And Liability [Line Items]
Total backlog	$ 157,531
Amounts included in contract liability at the beginning of period	$ 15,318
Within Next Twelve Months
Contract With Customer, Asset And Liability [Line Items]
Remaining performance obligation (as a precentage)	95.00%
By End of 2019
Contract With Customer, Asset And Liability [Line Items]
Remaining performance obligation (as a precentage)	3.00%