Fair Value Measurement (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Assets fair value	$ 83,983	$ 127,289
Level 1
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Assets fair value	18,850	77,522
Level 2
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Assets fair value	65,133	49,767
Money Market Funds
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Assets fair value	18,850	77,522
Money Market Funds | Level 1
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Assets fair value	18,850	77,522
Corporate debt securities
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Assets fair value	28,520	19,738
Corporate debt securities | Level 2
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Assets fair value	28,520	19,738
Commercial paper
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Assets fair value	24,187	16,393
Commercial paper | Level 2
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Assets fair value	24,187	16,393
Securities and obligations of U.S. government agencies
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Assets fair value	12,426	13,636
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	$ 13,636