Property and Equipment, Net (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Property and equipment	$ 141,660		$ 133,797
Less: accumulated depreciation and amortization	(80,964)		(75,240)
Property and equipment, net	60,696		58,557
Depreciation and amortization expense	6,400	$ 4,700
Capital leases, accumulated depreciation	200
Computer equipment
Property, Plant and Equipment [Line Items]
Property and equipment	80,215		77,883
Computer software
Property, Plant and Equipment [Line Items]
Property and equipment	21,176		20,447
Furniture, fixtures and equipment
Property, Plant and Equipment [Line Items]
Property and equipment	5,408		5,075
Assets under capital lease
Property, Plant and Equipment [Line Items]
Property and equipment	3,503		0
Scanner appliances
Property, Plant and Equipment [Line Items]
Property and equipment	15,010		14,325
Scanner appliances and other computer equipment subject to subscription
Property, Plant and Equipment [Line Items]
Property and equipment, net	6,900		6,800
Scanner appliances and other computer equipment not placed in service
Property, Plant and Equipment [Line Items]
Property and equipment	1,000		900
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment	$ 16,348		$ 16,067