Summary of Restructuring Reserve (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Restructuring And Related Activities [Abstract]
Restructuring reserve beginning balance	$ 1,588
Restructuring expenses incurred during the period	3,020	$ 3,651
Amounts paid during the period	(1,675)	(2,063)
Restructuring reserve ending balance	$ 2,933	$ 1,588