Fair Value Measurements - Recurring (Details) - Recurring - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Term Notes Payable
Fair Value Measurements
Liabilities, fair value	$ 15,000
Money market funds
Fair Value Measurements
Assets, fair value	11,850	$ 3,939
U.S. government agencies
Fair Value Measurements
Assets, fair value	1,202
Commercial paper
Fair Value Measurements
Assets, fair value	12,620
Level 1 | Money market funds
Fair Value Measurements
Assets, fair value	11,850	$ 3,939
Level 2 | Term Notes Payable
Fair Value Measurements
Liabilities, fair value	15,000
Level 2 | U.S. government agencies
Fair Value Measurements
Assets, fair value	1,202
Level 2 | Commercial paper
Fair Value Measurements
Assets, fair value	12,620
Level 3 | Term Notes Payable
Fair Value Measurements
Liabilities, fair value	$ 15,000