Fair Value Measurement of Cash Equivalents and Investments (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Fair Value, Assets and Liabilities
Cash and Cash Equivalents, Fair Value Disclosure	$ 26,791	$ 25,427
Investments, fair value disclosure	48,452	51,923
Money Market Funds | Level 1 Inputs
Fair Value, Assets and Liabilities
Cash and Cash Equivalents, Fair Value Disclosure	17,929	24,577
Investments, fair value disclosure	0	0
Agency Securities | Level 2 Inputs
Fair Value, Assets and Liabilities
Cash and Cash Equivalents, Fair Value Disclosure	0	0
Investments, fair value disclosure	16,882	19,623
Corporate Debt Securities | Level 2 Inputs
Fair Value, Assets and Liabilities
Cash and Cash Equivalents, Fair Value Disclosure	540	850
Investments, fair value disclosure	22,508	26,270
US Treasury and Government | Level 2 Inputs
Fair Value, Assets and Liabilities
Cash and Cash Equivalents, Fair Value Disclosure	0	0
Investments, fair value disclosure	6,539	5,531
Commercial Paper | Level 2 Inputs
Fair Value, Assets and Liabilities
Cash and Cash Equivalents, Fair Value Disclosure	8,322	0
Investments, fair value disclosure	$ 2,523	$ 499