Property and Equipment, Net (Details) - USD ($) $ in Thousands		12 Months Ended
	Nov. 20, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Sep. 30, 2018
Property, Plant and Equipment [Line Items]
Property and equipment			$ 133,797		$ 160,672
Less: accumulated depreciation and amortization			(75,240)		(99,230)
Property and equipment, net		$ 61,442	58,557		61,442
Depreciation and amortization expense		25,100	19,900	$ 16,600
Loss on disposal of office facilities	$ 200
Gross amount of abandoned costs	2,400
Accumulated depreciation on abandoned facility	$ 2,200
Computer equipment
Property, Plant and Equipment [Line Items]
Property and equipment			77,883		93,530
Computer software
Property, Plant and Equipment [Line Items]
Property and equipment			20,447		26,030
Furniture, fixtures and equipment
Property, Plant and Equipment [Line Items]
Property and equipment			5,075		5,814
Equipment Under Capital Lease [Member]
Property, Plant and Equipment [Line Items]
Property and equipment			0		3,503
Scanner appliances
Property, Plant and Equipment [Line Items]
Property and equipment			14,325		15,356
Scanner appliances and other computer equipment subject to subscription
Property, Plant and Equipment [Line Items]
Property and equipment, net		7,900	6,800
Scanner appliances and other computer equipment not placed in service
Property, Plant and Equipment [Line Items]
Property and equipment		1,800	900
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment			16,067		$ 16,439
Other fixed assets not placed in service
Property, Plant and Equipment [Line Items]
Property and equipment		$ 3,700	$ 9,600