Deferred Revenue and Customer Advances (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Jul. 01, 2018	Dec. 31, 2017	Oct. 01, 2017	Jul. 02, 2017	Dec. 31, 2016
Deferred Revenue Arrangement
Maintenance and training	$ 59,681		$ 57,256
Extended warranty	27,617	$ 25,971	24,438	$ 26,492	$ 29,377	$ 28,200
Customer advances, undelivered elements and other	20,042		32,047
Total deferred revenue and customer advances	$ 107,340		$ 113,741