Stockholders' Equity - Stock Option Activity (Details) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2017 USD ($) $ / shares shares
Equity [Abstract]
Unrecognized compensation cost, net of forfeitures | $	$ 4,400
Weighted average period to recognize stock compensation expense	1 year 7 months 6 days
Options
Outstanding, Beginning Balance | shares	6,447,594
Granted during period | shares	653,842
Exercised during period | shares	(7,757)
Expired during period | shares	(163,836)
Forfeited during period | shares	(68,875)
Outstanding, Ending Balance | shares	6,860,968
Weighted-Average Exercise Price
Outstanding, Beginning Balance | $ / shares	$ 6.41
Granted during period | $ / shares	2.17
Exercised during period | $ / shares	2.10
Expired during period | $ / shares	8.82
Forfeited during period | $ / shares	5.59
Outstanding, Ending Balance | $ / shares	$ 5.96
Additional disclosures
Options, Exercisable | shares	5,085,833
Weighted Average Exercise Price, Exercisable | $ / shares	$ 6.72
Weighted Average Remaining Contractual Term	6 years 3 months 7 days
Weighted Average Remaining Contractual Term exercisable at end of period	5 years 3 months 29 days
Aggregate Intrinsic Value | $	$ 282,786
Aggregate Intrinsic Value, exercisable at end of period | $	$ 29,895