Summary of Significant Accounting Policies - Transaction Price Allocated to Remaining Performance Obligations (Details) $ in Millions	Dec. 31, 2018 USD ($)
Fixed-price [Member]
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 13.2
Managed-support Contracts [Member]
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 38.8