Fair Value Measurement of Cash Equivalents and Investments (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Fair Value, Assets and Liabilities
Cash Equivalents, Fair Value	$ 20,808	$ 25,427
Investments, Fair Value	48,757	51,923
Money Market Funds | Level 1 Inputs
Fair Value, Assets and Liabilities
Cash Equivalents, Fair Value	20,808	24,577
Investments, Fair Value	0	0
Corporate Debt Securities | Level 2 Inputs
Fair Value, Assets and Liabilities
Cash Equivalents, Fair Value	0	850
Investments, Fair Value	21,672	26,270
Agency Securities | Level 2 Inputs
Fair Value, Assets and Liabilities
Cash Equivalents, Fair Value	0	0
Investments, Fair Value	17,149	19,623
US Treasury and Government | Level 2 Inputs
Fair Value, Assets and Liabilities
Cash Equivalents, Fair Value	0	0
Investments, Fair Value	6,537	5,531
Commercial Paper | Level 2 Inputs
Fair Value, Assets and Liabilities
Cash Equivalents, Fair Value	0	0
Investments, Fair Value	$ 3,399	$ 499