Summary of Significant Accounting Policies (Details) - USD ($)
$ in Thousands
3 Months Ended 12 Months Ended
Dec. 31, 2015
Sep. 30, 2015
Jun. 30, 2015
Mar. 31, 2015
Dec. 31, 2014
Sep. 30, 2014
Jun. 30, 2014
Mar. 31, 2014
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Summary of Significant Accounting Policies                        
Net loss $ 28,250 $ 6,604 $ 2,992 $ 3,384 $ 3,197 $ 1,452 $ 209 $ 953 $ 41,230 $ 5,811 $ 19,125  
Net cash provided by (used in) operations                 (18,184) 450 (25,877)  
Accumulated deficit 175,276       134,046       175,276 134,046    
Cash and cash equivalents $ 112,801       $ 96,729       $ 112,801 $ 96,729 $ 9,722 $ 39,208