Fair Value Measurements - Financial Assets and Liabilities Measured on a Recurring Basis at Fair Value (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Mutual fund assets	$ 28,270	$ 24,055
Derivative assets:
Foreign currency contracts	335	453
Total assets at fair value	28,605	24,508
Derivative liabilities:
Foreign currency contracts	94	469
Total liabilities at fair value		469
Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Mutual fund assets	28,270	24,055
Derivative assets:
Total assets at fair value	28,270	24,055
Level 2 [Member]
Derivative assets:
Foreign currency contracts	335	453
Total assets at fair value	335	453
Derivative liabilities:
Foreign currency contracts	$ 94	469
Total liabilities at fair value		$ 469