Fair Value Measurements - Summary of Fair Value Assets and Liabilities Measured on Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Assets
Assets fair value	$ 152,555
Money market funds
Assets
Assets fair value	136,481	$ 111,533
Fair Value Measurements on Recurring Basis | Level 1
Assets
Assets fair value	136,481
Fair Value Measurements on Recurring Basis | Level 1 | Money market funds
Assets
Assets fair value	136,481	$ 111,533
Fair Value Measurements on Recurring Basis | Level 2
Assets
Assets fair value	16,074
U.S. government agency obligations
Assets
Assets fair value	12,075
U.S. government agency obligations | Fair Value Measurements on Recurring Basis | Level 2
Assets
Assets fair value	12,075
Corporate securities
Assets
Assets fair value	3,999
Corporate securities | Fair Value Measurements on Recurring Basis | Level 2
Assets
Assets fair value	$ 3,999