Fair Value Measurements - Financial Assets and Liabilities Measured at Fair Value (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Assets:
Total cash equivalents		$ 282,358
Total assets	$ 534,281
Liabilities:
Total liabilities	106,175
Foreign exchange contracts
Assets:
Foreign exchange contracts	111,235
Liabilities:
Foreign exchange contracts contracts	106,175
Derivative, Collateral, Obligation to Return Cash	20,272
Cash collateral paid for foreign exchange derivatives	33,911
Repurchase agreements
Assets:
Total cash equivalents	363,335	232,131
Money market
Assets:
Total cash equivalents	50,341	50,179
Certificates of deposit
Assets:
Total cash equivalents	9,370	48
Level 1
Assets:
Total cash equivalents		0
Total assets	28
Liabilities:
Total liabilities	353
Level 1 | Foreign exchange contracts
Assets:
Foreign exchange contracts	28
Liabilities:
Foreign exchange contracts contracts	353
Level 2
Assets:
Total cash equivalents		282,358
Total assets	534,253
Liabilities:
Total liabilities	105,822
Level 2 | Foreign exchange contracts
Assets:
Foreign exchange contracts	111,207
Liabilities:
Foreign exchange contracts contracts	105,822
Level 2 | Repurchase agreements
Assets:
Total cash equivalents	363,335	232,131
Level 2 | Money market
Assets:
Total cash equivalents	50,341	50,179
Level 2 | Certificates of deposit
Assets:
Total cash equivalents	$ 9,370	$ 48