Restructuring Charges - Schedule of Changes in Future Minimum Lease Obligations (Detail) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Restructuring And Related Activities [Abstract]
Balance, Beginning of Period		$ 15,843	$ 34,410	$ 20,763	$ 36,814
Charges Incurred	[1]	5,165	749	5,597	5,206
Net Cash Payments		(6,722)	(8,403)	(12,074)	(14,402)
Other	[2]	41	353	41	(509)
Balance, End of Period		$ 14,327	$ 27,109	$ 14,327	$ 27,109

[1] Includes charges for newly vacated spaces and subsequent adjustments for accretion, revised estimates and variances between estimated and actual charges, net of any reversals for terminated lease obligations.

[2] Includes existing prepaid rent and deferred rent liability balances for newly vacated spaces that offset the losses incurred in the period recorded.