Short-term Investments (Details) $ in Thousands	Jun. 30, 2017 USD ($)
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 41,890
Unrealized Gains	52
Unrealized Losses	(73)
Fair Value	41,869
U.S. government securities
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	21,910
Unrealized Gains	52
Unrealized Losses	(73)
Fair Value	21,889
Commercial paper
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	6,980
Unrealized Gains	0
Unrealized Losses	0
Fair Value	6,980
Repurchase agreement
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	13,000
Unrealized Gains	0
Unrealized Losses	0
Fair Value	$ 13,000