Restructuring Charges - Schedule of Changes in Future Minimum Lease Obligations (Detail) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Restructuring And Related Activities [Abstract]
Balance, Beginning of Period		$ 14,327	$ 27,109	$ 20,763	$ 36,814
Charges Incurred	[1]	2,304	9,422	7,901	14,628
Net Cash Payments		(5,388)	(9,094)	(17,462)	(23,496)
Other	[2]		2,932	41	2,423
Balance, End of Period		$ 11,243	$ 30,369	$ 11,243	$ 30,369

[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.