Summary of Significant Accounting Policies (Additional Capital) (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
Policies
Net (loss) income	$ (22,960)	$ (17,630)	$ (19,681)	$ (10,004)	$ 1,254	$ 3,724	$ (514)	$ (9,616)	$ (70,275)	$ (5,152)	$ (37,110)
Accumulated deficit	250,083				179,808				250,083	179,808
Cash and cash equivalents	28,947				87,176				28,947	87,176	$ 30,496	$ 5,747
Short-term investments	201,586								201,586
Restricted cash
Restricted cash, current portion	901				503				901	503
Restricted cash, long term portion	683				$ 808				683	$ 808
Corporate Headquarters Lease
Restricted cash
Restricted cash, current portion	800								800
Restricted cash, long term portion	300								300
Cancellation of Service
Restricted cash
Restricted cash, current portion	100								100
Credit Card
Restricted cash
Restricted cash, long term portion	$ 400								$ 400