Other Balance Sheet Amounts - Property and Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 52,797	$ 46,699
Less: accumulated depreciation and amortization	(31,980)	(22,737)
Total property and equipment, net	20,817	23,962
Depreciation expense	$ 10,300	9,900	$ 7,600
Minimum
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	2 years
Maximum
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	7 years
Computer equipment and software
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 38,838	32,926
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
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 3,855	3,837
Property and equipment, useful life	7 years
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 10,046	9,878
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]
Property and equipment, gross	$ 58	$ 58