Revenue - Performance Obligation (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($)
Revenue, Performance Obligation [Abstract]
Unsatisfied or partially unsatisfied performance obligations	$ 2,762,593
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2018-04-01
Revenue, Performance Obligation [Abstract]
Unsatisfied or partially unsatisfied performance obligations	$ 613,877
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	8 months
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-01-01
Revenue, Performance Obligation [Abstract]
Unsatisfied or partially unsatisfied performance obligations	$ 625,501
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	12 months
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-01-01
Revenue, Performance Obligation [Abstract]
Unsatisfied or partially unsatisfied performance obligations	$ 534,100
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	12 months
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-01-01
Revenue, Performance Obligation [Abstract]
Unsatisfied or partially unsatisfied performance obligations	$ 440,213
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	12 months
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-01-01
Revenue, Performance Obligation [Abstract]
Unsatisfied or partially unsatisfied performance obligations	$ 548,902
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	84 months