Summary of Cash, Cash Equivalents, Short-Term investments, and Restricted Cash and Investments - Summary of cash, cash equivalents, short-term investments and restricted cash and investments (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015	Dec. 31, 2014
Cash and cash equivalents:
Cash	$ 30,782	$ 29,133
Cash equivalents	31,957	46,955
Cash and cash equivalents	62,739	76,088	$ 62,002	$ 43,035
Short-term investments	38,364	23,294
Restricted cash and investments:
Restricted cash and investments, current	$ 2,659	$ 2,660