Restructuring Activities - Summary of Charges Related to Restructuring Activities (Detail) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended		12 Months Ended
	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Restructuring Cost And Reserve [Line Items]
Accrued Restructuring Expenses				$ 921	$ 628	$ 628
Expenses			$ 0	4,890	0
Less: Payments	$ (3,800)	$ (400)	$ (200)	(4,755)	(628)	(900)
Accrued Restructuring Expenses	1,056	921		1,056		921
Severance Benefits and Related Costs Due to Workforce Reduction [Member]
Restructuring Cost And Reserve [Line Items]
Accrued Restructuring Expenses				921	628	628
Expenses				4,890
Less: Payments				(4,755)	$ (628)
Accrued Restructuring Expenses	$ 1,056	$ 921		$ 1,056		$ 921