Fair Value Measurement (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Financial and nonfinancial liabilities measured at fair value	$ 0	$ 0
Nonfinancial assets measured at fair value	0	0
Assets fair value	70,742	73,220
Level 1
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Assets fair value	12,065	15,003
Level 2
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Assets fair value	58,677	58,217
Money Market Funds
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Assets fair value	12,065	15,003
Money Market Funds | Level 1
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Assets fair value	12,065	15,003
Corporate debt securities
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Assets fair value	5,525	10,738
Corporate debt securities | Level 2
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Assets fair value	5,525	10,738
Commercial paper
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Assets fair value	52,252	47,479
Commercial paper | Level 2
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Assets fair value	52,252	$ 47,479
Government debt securities
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Assets fair value	900
Government debt securities | Level 2
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Assets fair value	$ 900