Property and Equipment, Net (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Property, Plant and Equipment [Line Items]
Property and equipment	$ 98,906	$ 89,474
Less: accumulated depreciation and amortization	(59,505)	(58,145)
Property and equipment, net	39,401	31,329
Depreciation and amortization expense	16,600	13,900	$ 11,500
Computer equipment
Property, Plant and Equipment [Line Items]
Property and equipment	57,295	48,192
Computer software
Property, Plant and Equipment [Line Items]
Property and equipment	19,716	12,484
Furniture, fixtures and equipment
Property, Plant and Equipment [Line Items]
Property and equipment	3,425	2,804
Scanner appliances
Property, Plant and Equipment [Line Items]
Property and equipment	14,776	22,627
Scanner appliances and other computer equipment subject to subscription
Property, Plant and Equipment [Line Items]
Property and equipment, net	8,300	8,400
Scanner appliances and other computer equipment not placed in service
Property, Plant and Equipment [Line Items]
Property and equipment	1,300	1,400
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment	3,694	3,367
Other fixed assets not placed in service
Property, Plant and Equipment [Line Items]
Property and equipment	$ 3,600	$ 4,300