Fair Value Measurements - Summary of Fair Value Assets Measured on Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Assets
Assets fair value	$ 429,285	$ 393,906
Money market funds
Assets
Assets fair value	100,441	245,194
Fair Value Measurements on Recurring Basis | Level 1
Assets
Assets fair value	100,441	245,194
Fair Value Measurements on Recurring Basis | Level 2
Assets
Assets fair value	328,844	148,712
Fair Value Measurements on Recurring Basis | Money market funds | Level 1
Assets
Assets fair value	100,441	245,194
U.S. government agency obligations
Assets
Assets fair value	134,055	85,033
U.S. government agency obligations | Fair Value Measurements on Recurring Basis | Level 2
Assets
Assets fair value	134,055	85,033
Corporate securities
Assets
Assets fair value	194,789	63,679
Corporate securities | Fair Value Measurements on Recurring Basis | Level 2
Assets
Assets fair value	$ 194,789	$ 63,679