Restructuring Charges - Accrual for Severance and Related Costs (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		$ 721	$ 4,969	$ 2,170	$ 8,686
Severance & Related Charges		1,898		1,898
Payments		(273)	(1,715)	(1,607)	(5,166)
Non-cash Adjustments	[1]	(46)	23	(161)	(243)
Balance, End of Period		$ 2,300	$ 3,277	$ 2,300	$ 3,277

[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.