Income Taxes - Components (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Current:      
U.S. federal $ 123 $ 0 $ 0
State (26) 0 0
Provision for income taxes $ 149 $ 0 $ 0