Fair Value Measurement (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Assets:
Marketable securities	$ 82,446	$ 82,664
Liabilities:
Foreign exchange contracts	84
Government bonds
Assets:
Marketable securities	489	495
Certificates of deposits
Assets:
Marketable securities	747	747
Corporate bonds
Assets:
Marketable securities	81,210	81,422
Level II
Liabilities:
Foreign exchange contracts	84
Level II | Government bonds
Assets:
Marketable securities	489	495
Level II | Certificates of deposits
Assets:
Marketable securities	747	747
Level II | Corporate bonds
Assets:
Marketable securities	$ 81,210	$ 81,422