Cash and Cash Equivalents and Short Term Investments - Summary of Cash and Cash Equivalents (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Cash And Cash Equivalents [Line Items]
Total cash and cash equivalents	$ 119,423	$ 57,613	$ 175,894	$ 34,891
Cash
Cash And Cash Equivalents [Line Items]
Total cash and cash equivalents	75,421	47,614
Money market funds
Cash And Cash Equivalents [Line Items]
Total cash and cash equivalents	$ 44,002
U.S. treasury bills
Cash And Cash Equivalents [Line Items]
Total cash and cash equivalents		$ 9,999