Fair Value of Financial Instruments (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Total
Assets:
Money market funds (cash equivalents)	$ 13,127	$ 27,096
Corporate notes and bonds	12,974	11,460
Asset-backed securities	141	500
Total assets measured at fair value	26,242	39,056
Significant Unobservable Inputs (Level 3)
Assets:
Money market funds (cash equivalents)
Corporate notes and bonds
Asset-backed securities
Total assets measured at fair value
Significant Other Observable Inputs (Level 2)
Assets:
Money market funds (cash equivalents)
Corporate notes and bonds	12,974	11,460
Asset-backed securities	141	500
Total assets measured at fair value	13,115	11,960
Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Money market funds (cash equivalents)	13,127	27,096
Corporate notes and bonds
Asset-backed securities
Total assets measured at fair value	$ 13,127	$ 27,096