Stock-based Compensation - Stock Option Activity (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Stock options
Outstanding
Options granted (in shares)	0
2003 Stock Incentive Plan, as amended and restated
Outstanding
Beginning balance (in shares)	28	12
Options granted (in shares)		16
Ending balance (in shares)	28	28
Exercisable (in shares)	17
Vested and expected to vest (in shares)	28
Weighted-Average Exercise Price
Options granted (in dollars per share)		$ 164,566.19
Outstanding (in dollars per share)	$ 2,957,210.16	$ 2,957,210.16	$ 6,448,015.13
Exercisable (in dollars per share)	4,579,286.97
Vested and expected to vest (in dollars per share)	$ 2,957,210.16
Weighted-Average Remaining Contractual Term
Outstanding	7 years 7 months 6 days
Exercisable	7 years 7 months 6 days
Vested and expected to vest	7 years 10 months 24 days
Intrinsic value
Outstanding (in dollars)	$ 0
Exercisable (in dollars)	0
Vested and expected to vest (in dollars)	$ 0
Inducement grants
Outstanding
Beginning balance (in shares)	18	8
Options granted (in shares)		10
Ending balance (in shares)	18	18
Exercisable (in shares)	18
Vested and expected to vest (in shares)	18
Weighted-Average Exercise Price
Options granted (in dollars per share)		$ 113,808.24
Outstanding (in dollars per share)	$ 352,876.06	$ 352,876.06	$ 651,710.83
Exercisable (in dollars per share)	352,876.06
Vested and expected to vest (in dollars per share)	$ 352,876.06
Weighted-Average Remaining Contractual Term
Outstanding	8 years 1 month 6 days
Exercisable	8 years 1 month 6 days
Vested and expected to vest	8 years 1 month 6 days
Intrinsic value
Outstanding (in dollars)	$ 0
Exercisable (in dollars)	0
Vested and expected to vest (in dollars)	$ 0