Restructuring and Asset Impairment Charges (Detail) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
Restructuring Reserve [Roll Forward]
Accrued restructuring, beginning balance	$ 809	$ 558
Restructuring expenses		4,683
Cash payments	(359)	(4,432)
Accrued restructuring, ending balance	450	809
Contract termination costs
Restructuring Reserve [Roll Forward]
Accrued restructuring, beginning balance	467	558
Restructuring expenses		0
Cash payments	(46)	(91)
Accrued restructuring, ending balance	421	467
Employee severance and termination benefits
Restructuring Reserve [Roll Forward]
Accrued restructuring, beginning balance	342	0
Restructuring expenses		4,683
Cash payments	(313)	(4,341)
Accrued restructuring, ending balance	$ 29	$ 342