Fair Value Measurements - Recurring (Details) - Recurring - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Money market funds
Fair Value Measurements
Assets, fair value	$ 24,841	$ 10,601
Government and agency securities
Fair Value Measurements
Assets, fair value		1,201
Corporate debt securities
Fair Value Measurements
Assets, fair value	15,162	6,589
Level 1 | Money market funds
Fair Value Measurements
Assets, fair value	24,841	10,601
Level 2 | Government and agency securities
Fair Value Measurements
Assets, fair value		1,201
Level 2 | Corporate debt securities
Fair Value Measurements
Assets, fair value	$ 15,162	$ 6,589