Restructuring Activities - Summary of Charges Related to Restructuring Activities (Detail) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2017
Restructuring Cost And Reserve [Line Items]
Accrued Restructuring Expenses		$ 628	$ 774
Expenses		1,289	9,521
Less: Payments	$ (400)	(996)	(9,667)
Accrued Restructuring Expenses	921	921	628
Severance Benefits and Related Costs Due to Workforce Reduction [Member]
Restructuring Cost And Reserve [Line Items]
Accrued Restructuring Expenses		628	774
Expenses		1,289	9,521
Less: Payments		(996)	(9,667)
Accrued Restructuring Expenses	$ 921	$ 921	$ 628