Fair Value Measurement (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Financial and nonfinancial liabilities measured at fair value	$ 0
Nonfinancial assets measured at fair value	0
Assets fair value	73,220	$ 83,983
Level 1
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Assets fair value	15,003	18,850
Level 2
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Assets fair value	58,217	65,133
Money Market Funds
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Assets fair value	15,003	18,850
Money Market Funds | Level 1
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Assets fair value	15,003	18,850
Corporate debt securities
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Assets fair value	10,738	28,520
Corporate debt securities | Level 2
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Assets fair value	10,738	28,520
Commercial paper
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Assets fair value	47,479	24,187
Commercial paper | Level 2
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Assets fair value	$ 47,479	24,187
Securities and obligations of U.S. government agencies
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Assets fair value		12,426
Securities and obligations of U.S. government agencies | Level 2
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Assets fair value		$ 12,426