Fair Value Measurements - Schedule of Assets and Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Assets:
Aggregate Fair Value	$ 419,626	$ 375,793
Foreign currency derivative contracts		85
Total	530,827	446,030
Liabilities:
Foreign currency derivative contracts	108	8
Total	108	8
Money market funds
Assets:
Cash equivalents	111,201	54,163
U.S. government treasuries
Assets:
Cash equivalents		15,989
Short-term marketable securities: | U.S. government treasuries
Assets:
Aggregate Fair Value	333,212	250,070
Short-term marketable securities: | U.S. government agency securities
Assets:
Aggregate Fair Value		2,000
Short-term marketable securities: | Corporate debt securities
Assets:
Aggregate Fair Value	49,761	53,479
Short-term marketable securities: | Commercial paper
Assets:
Aggregate Fair Value	29,424	30,358
Long-term marketable securities: | U.S. government treasuries
Assets:
Aggregate Fair Value		13,869
Long-term marketable securities: | Corporate debt securities
Assets:
Aggregate Fair Value	7,229	26,017
Level 1
Assets:
Foreign currency derivative contracts		0
Total	444,413	334,091
Liabilities:
Foreign currency derivative contracts	0	0
Total	0	0
Level 1 | Money market funds
Assets:
Cash equivalents	111,201	54,163
Level 1 | U.S. government treasuries
Assets:
Cash equivalents		15,989
Level 1 | Short-term marketable securities: | U.S. government treasuries
Assets:
Aggregate Fair Value	333,212	250,070
Level 1 | Short-term marketable securities: | U.S. government agency securities
Assets:
Aggregate Fair Value		0
Level 1 | Short-term marketable securities: | Corporate debt securities
Assets:
Aggregate Fair Value	0	0
Level 1 | Short-term marketable securities: | Commercial paper
Assets:
Aggregate Fair Value	0	0
Level 1 | Long-term marketable securities: | U.S. government treasuries
Assets:
Aggregate Fair Value		13,869
Level 1 | Long-term marketable securities: | Corporate debt securities
Assets:
Aggregate Fair Value	0	0
Level 2
Assets:
Foreign currency derivative contracts		85
Total	86,414	111,939
Liabilities:
Foreign currency derivative contracts	108	8
Total	108	8
Level 2 | Money market funds
Assets:
Cash equivalents	0	0
Level 2 | U.S. government treasuries
Assets:
Cash equivalents		0
Level 2 | Short-term marketable securities: | U.S. government treasuries
Assets:
Aggregate Fair Value	0	0
Level 2 | Short-term marketable securities: | U.S. government agency securities
Assets:
Aggregate Fair Value		2,000
Level 2 | Short-term marketable securities: | Corporate debt securities
Assets:
Aggregate Fair Value	49,761	53,479
Level 2 | Short-term marketable securities: | Commercial paper
Assets:
Aggregate Fair Value	29,424	30,358
Level 2 | Long-term marketable securities: | U.S. government treasuries
Assets:
Aggregate Fair Value		0
Level 2 | Long-term marketable securities: | Corporate debt securities
Assets:
Aggregate Fair Value	7,229	26,017
Level 3
Assets:
Foreign currency derivative contracts		0
Total	0	0
Liabilities:
Foreign currency derivative contracts	0	0
Total	0	0
Level 3 | Money market funds
Assets:
Cash equivalents	0	0
Level 3 | U.S. government treasuries
Assets:
Cash equivalents		0
Level 3 | Short-term marketable securities: | U.S. government treasuries
Assets:
Aggregate Fair Value	0	0
Level 3 | Short-term marketable securities: | U.S. government agency securities
Assets:
Aggregate Fair Value		0
Level 3 | Short-term marketable securities: | Corporate debt securities
Assets:
Aggregate Fair Value	0	0
Level 3 | Short-term marketable securities: | Commercial paper
Assets:
Aggregate Fair Value	0	0
Level 3 | Long-term marketable securities: | U.S. government treasuries
Assets:
Aggregate Fair Value		0
Level 3 | Long-term marketable securities: | Corporate debt securities
Assets:
Aggregate Fair Value	$ 0	$ 0