Employee Benefit Plans - Stock Activity, Weighted Average Exercise Price (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Shares
Granted (in shares)	3,702,500	3,960,000	4,245,000
Stock options
Shares
Options outstanding, beginning balance (in shares)	11,700,786
Granted (in shares)	3,702,500	3,960,000	4,246,000
Exercised (in shares)	(274,000)
Forfeited (in shares)	(347,482)
Expired (in shares)	(21,750)
Options outstanding, end balance (in shares)	14,760,054	11,700,786
Options exercisable (in shares)	7,368,564
Options unvested (in shares)	7,391,490
Weighted Average Exercise Price
Options outstanding, beginning balance, weighted-average exercise price	$ 3.29
Granted, weighted-average exercise price	1.72
Exercised, weighted-average exercise price	0.37
Forfeited, weighted-average exercise price	2.91
Expired, weighted-average exercise price	49.18
Options outstanding, end balance, weighted-average exercise price	2.90	$ 3.29
Options exercisable, weighted-average exercise price	3.28
Options unvested, weighted-average exercise price	$ 2.52
Stock option activity additional disclosures
Options outstanding, weighted-average remaining contractual term	7 years 10 months 24 days	8 years 3 months 18 days
Options exercisable, weighted-average remaining contractual term	7 years
Options unvested, weighted-average remaining contractual term	8 years 10 months 24 days
Options outstanding, aggregate intrinsic value	$ 878
Options exercisable, aggregate intrinsic value	$ 878
Weighted-average grant date fair value of options granted (per share)	$ 1.39	$ 1.99	$ 4.05
Unrecognized compensation cost	$ 11,000
Period for recognition	3 years
Fair value of stock options that vested during the period	$ 8,600	$ 6,100
the 2011 Plan | Stock options
Shares
Options outstanding, end balance (in shares)	14,800,000