Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Fair Value Assets Measured On Recurring Basis [Line Items]
Total cash equivalents	$ 28,382	$ 5,070
Total investments	38,299	75,109
Total assets measured at fair value	66,681	80,179
Level 1
Fair Value Assets Measured On Recurring Basis [Line Items]
Total cash equivalents	28,382	4,071
Total assets measured at fair value	28,382	4,071
Level 2
Fair Value Assets Measured On Recurring Basis [Line Items]
Total cash equivalents		999
Total investments	38,299	75,109
Total assets measured at fair value	38,299	76,108
Money market funds
Fair Value Assets Measured On Recurring Basis [Line Items]
Total cash equivalents	28,382	4,071
Money market funds | Level 1
Fair Value Assets Measured On Recurring Basis [Line Items]
Total cash equivalents	28,382	4,071
Commercial paper
Fair Value Assets Measured On Recurring Basis [Line Items]
Total cash equivalents		999
Total investments	17,852	27,846
Commercial paper | Level 2
Fair Value Assets Measured On Recurring Basis [Line Items]
Total cash equivalents		999
Total investments	17,852	27,846
Corporate debt securities
Fair Value Assets Measured On Recurring Basis [Line Items]
Total investments	17,936	45,830
Corporate debt securities | Level 2
Fair Value Assets Measured On Recurring Basis [Line Items]
Total investments	17,936	45,830
Municipal bonds
Fair Value Assets Measured On Recurring Basis [Line Items]
Total investments	2,511	1,433
Municipal bonds | Level 2
Fair Value Assets Measured On Recurring Basis [Line Items]
Total investments	$ 2,511	$ 1,433