Fair Value Measurements - Financial Assets and Liabilities Measured at Fair Value (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Assets:
Cash and cash equivalents		$ 282,358
Foreign exchange contracts	$ 39,000
Total cash equivalents	517,723
Cash collateral obligation for foreign exchange contracts	12,500
Liabilities:
Foreign exchange contracts	26,900
Total liabilities	26,888
Cash collateral obligation for foreign exchange contracts	10,900
Repurchase agreements
Assets:
Cash and cash equivalents	420,838	232,131
Money market
Assets:
Cash and cash equivalents	50,423	50,179
Certificates of deposit
Assets:
Cash and cash equivalents	7,417	48
Level 1
Assets:
Total cash equivalents	10
Liabilities:
Total liabilities	67
Level 2
Assets:
Cash and cash equivalents		282,358
Total cash equivalents	517,713
Liabilities:
Total liabilities	26,821
Level 2 | Repurchase agreements
Assets:
Cash and cash equivalents	420,838	232,131
Level 2 | Money market
Assets:
Cash and cash equivalents	50,423	50,179
Level 2 | Certificates of deposit
Assets:
Cash and cash equivalents	7,417	$ 48
Foreign exchange contracts
Assets:
Foreign exchange contracts	39,045
Cash collateral obligation for foreign exchange contracts	12,540
Liabilities:
Foreign exchange contracts	26,888
Cash collateral obligation for foreign exchange contracts	10,882
Foreign exchange contracts | Level 1
Assets:
Foreign exchange contracts	10
Liabilities:
Foreign exchange contracts	67
Foreign exchange contracts | Level 2
Assets:
Foreign exchange contracts	39,035
Liabilities:
Foreign exchange contracts	$ 26,821