Fair Value Measurements - Financial Assets and Liabilities Measured on a Recurring Basis at Fair Value (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Mutual fund assets	$ 28,055	$ 28,270
Derivative assets:
Foreign currency contracts	248	335
Total assets at fair value	28,303	28,605
Derivative liabilities:
Foreign currency contracts	71	94
Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Mutual fund assets	28,055	28,270
Derivative assets:
Total assets at fair value	28,055	28,270
Level 2 [Member]
Derivative assets:
Foreign currency contracts	248	335
Total assets at fair value	248	335
Derivative liabilities:
Foreign currency contracts	$ 71	$ 94