Fair Value Measurements - Assets (Details) $ in Thousands	Jun. 30, 2017 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Amount of transfers of financial assets between Level 1 and Level 2 measures	$ 0
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Short term investments	24,900
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Short term investments	$ 10,600