Employee Benefit Plans - Stock Activity, Weighted Average Exercise Price (Details) - Stock options - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Shares
Options outstanding, beginning balance (in shares)	8,367,271
Granted (in shares)	3,960,000	4,246,000	3,090,900
Exercised (in shares)	(173,334)
Forfeited (in shares)	(406,975)
Expired (in shares)	(46,176)
Options outstanding, end balance (in shares)	11,700,786	8,367,271
Options exercisable (in shares)	4,273,425
Options unvested (in shares)	7,427,361
Weighted Average Exercise Price
Options outstanding, beginning balance, weighted-average exercise price	$ 3.94
Granted, weighted-average exercise price	2.46
Exercised, weighted-average exercise price	0.96
Forfeited, weighted-average exercise price	3.18
Expired, weighted-average exercise price	59.35
Options outstanding, end balance, weighted-average exercise price	3.29	$ 3.94
Options exercisable, weighted-average exercise price	3.66
Options unvested, weighted-average exercise price	$ 3.08
Stock option activity additional disclosures
Options outstanding, weighted-average remaining contractual term	8 years 3 months 18 days	8 years 8 months 12 days
Options exercisable, weighted-average remaining contractual term	7 years 2 months 12 days
Options unvested, weighted-average remaining contractual term	9 years
Options outstanding, aggregate intrinsic value	$ 3,397
Options exercisable, aggregate intrinsic value	3,159
Options unvested, aggregate intrinsic value	$ 815
Weighted-average grant date fair value of options granted (per share)	$ 1.99	$ 4.05	$ 0.32
Unrecognized compensation cost	$ 14,900
Period for recognition	3 years
Fair value of stock options that vested during the period	$ 6,100	$ 3,400
the 2011 Plan
Shares
Options outstanding, end balance (in shares)	11,700,000