Stock-Based Compensation - Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Stock-based compensation expense
Total stock-based compensation expense	$ 25,914	$ 11,683	$ 7,759
Research and Development Expense
Stock-based compensation expense
Total stock-based compensation expense	11,082	4,954	2,034
General and Administrative Expense.
Stock-based compensation expense
Total stock-based compensation expense	$ 14,832	$ 6,729	$ 5,725