Restructuring - Activity in Restructuring Liability Accounts (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($)
Restructuring Cost and Reserve [Line Items]
Beginning Balance	$ 1,960
Provision, net	(145)
Usage	(1,111)
Ending Balance	704
Lease/Rental Terminations [Member]
Restructuring Cost and Reserve [Line Items]
Beginning Balance	1,786
Provision, net	(778)
Usage	(304)
Ending Balance	704
One-Time Employee Termination Benefits [Member]
Restructuring Cost and Reserve [Line Items]
Beginning Balance	65
Provision, net	721
Usage	(786)
Datacenter Consolidation, Other [Member]
Restructuring Cost and Reserve [Line Items]
Beginning Balance	109
Provision, net	(88)
Usage	$ (21)