Information about Contract Liabilities (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Deferred revenue and customer advances	$ 77,953		$ 83,614
Long-term deferred revenue and customer advances	29,387		$ 30,127
ASU 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Deferred revenue and customer advances	73,128	$ 76,638
Long-term deferred revenue and customer advances	19,419	20,848
ASU 2014-09 | Adjustments to Recognize Under Legacy GAAP
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Deferred revenue and customer advances	(4,825)	1,315
Long-term deferred revenue and customer advances	$ (9,968)	$ 8,539