Stockholders' Equity (Details) - shares	Jun. 30, 2016	Dec. 31, 2015
Common Stock
Options issued and outstanding (in shares)	5,362,144	4,179,521
Shares available for issuance	876,886	1,058,359
Total number of shares reserved for issuance	6,923,302	5,987,880
Shares of common stock subject to outstanding options
Common Stock
Shares available for issuance	876,886	1,058,359
ESPP
Common Stock
Shares available for issuance	684,272	750,000