Contingencies - Additional Information (Detail) $ in Thousands				1 Months Ended	2 Months Ended	12 Months Ended
	Dec. 29, 2017 USD ($)	Feb. 11, 2016 USD ($)	Dec. 17, 2015 USD ($)	Dec. 31, 2015 USD ($)	Dec. 29, 2017 USD ($)	Dec. 31, 2015 USD ($) assembled_workforce acquisition	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Loss Contingencies [Line Items]
Value of the service guarantee				$ 1,000		$ 1,000
Accrued liability for legal settlement				18,750		$ 18,750	$ 20,000
Number of assembled workforces | assembled_workforce						2
Number of asset acquisitions | acquisition						2
Payments to acquire employment relationships						$ 925	$ 0	$ 0
Settled litigation | FTC Contempt Action
Loss Contingencies [Line Items]
Payments for legal settlements			$ 100,000	100,000
Settlement amount			100,000	(116,000)
Amount distributed to the overseeing court			68,000
Amount authorized to fund consumer redress by any states' attorneys general			$ 32,000
Pending litigation | FTC Contempt Action
Loss Contingencies [Line Items]
Loss contingency accrual				3,000		3,000
Pending litigation | Ebarle Class Action
Loss Contingencies [Line Items]
Loss contingency accrual				13,000		13,000
Unfavorable regulatory action | Pending litigation | Lifelock vs. Etan Goldman
Loss Contingencies [Line Items]
Accrued liability for legal settlement				$ 2,500		2,500
Employment Contracts
Loss Contingencies [Line Items]
Payments to acquire employment relationships						$ 1,000
Term of employment required for contingency payment						2 years
Subsequent Event | Settled litigation | Ebarle Class Action
Loss Contingencies [Line Items]
Amount distributed to the overseeing court		$ 68,000
Forecast | Employment Contracts
Loss Contingencies [Line Items]
Contingency payment to be paid if acquired employees remain employed on anniversary	$ 100				$ 1,200