Other Balance Sheet Amounts - Property and Equipment (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Jan. 01, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 79,315		$ 79,315			$ 119,451
Less: accumulated depreciation and amortization	(43,575)		(43,575)			(42,197)
Total property and equipment, net	35,740		35,740			77,254
Leasehold improvements on build to suit property de-recognized					$ 5,000
Depreciation expense	3,000	$ 2,800	5,700	$ 5,300
Computer equipment and software
Property, Plant and Equipment [Line Items]
Total property and equipment	52,756		$ 52,756			52,055
Computer equipment and software | Minimum
Property, Plant and Equipment [Line Items]
Property and equipment, useful life			3 years
Computer equipment and software | Maximum
Property, Plant and Equipment [Line Items]
Property and equipment, useful life			5 years
Build to suit property
Property, Plant and Equipment [Line Items]
Total property and equipment	0		$ 0			51,058
Property and equipment, useful life			25 years
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Total property and equipment	5,303		$ 5,303			4,367
Property and equipment, useful life			7 years
Leasehold improvements
Property, Plant and Equipment [Line Items]
Total property and equipment	16,645		$ 16,645			9,987
Leasehold improvements | Minimum
Property, Plant and Equipment [Line Items]
Property and equipment, useful life			2 years
Leasehold improvements | Maximum
Property, Plant and Equipment [Line Items]
Property and equipment, useful life			6 years
Renovation in progress
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 4,611		$ 4,611			$ 1,984