Restructuring Charges - Accrual for Severance and Related Costs (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		$ 1,174	$ 6,624	$ 2,170	$ 8,686
Payments		(417)	(1,562)	(1,334)	(3,451)
Non-cash Adjustments	[1]	(36)	(93)	(115)	(266)
Balance, End of Period		$ 721	$ 4,969	$ 721	$ 4,969

[1] Includes cancellations due to employee departures prior to agreed upon end dates, employee transfers to open positions within the organization and subsequent adjustments to severance and related costs.