Leases - Additional Information (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($) ft²	Dec. 31, 2018 USD ($)
Operating Leased Assets [Line Items]
Operating lease, right of use asset	$ 87,743	$ 0
Operating lease, liability	115,763
UNITED STATES
Operating Leased Assets [Line Items]
Operating lease, right of use asset	74,300
Operating lease, liability	101,600
UNITED STATES | Northern Virginia Office Space
Operating Leased Assets [Line Items]
Operating lease, right of use asset	69,500
Operating lease, liability	$ 96,700
Area of office space | ft²	214,000
Lease term expiration date	Dec. 31, 2030
Lease option to extend, description	Option for the Company to extend the term for an additional ten or five consecutive years
UNITED STATES | Minimum | Northern Virginia Office Space
Operating Leased Assets [Line Items]
Lease extension term	5 years
UNITED STATES | Maximum | Northern Virginia Office Space
Operating Leased Assets [Line Items]
Lease extension term	10 years
Non-US
Operating Leased Assets [Line Items]
Operating lease, right of use asset	$ 13,400
Operating lease, liability	$ 14,200