Stock Incentive Plans - Summary of Stock Incentive Plans (Details) - USD ($)		9 Months Ended		12 Months Ended
	May 12, 2015	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Jun. 29, 2018
Shares Available for Grant
Ending balance (in shares)		238,172	513,385
Stock Options Outstanding
Ending balance (in shares)		2,868,868	2,984,304
RSUs Outstanding
Ending balance (in shares)		392,904	392,923
Options vested, exercisable and expected to vest
Weighted average grant date fair value of stock options granted (in dollars per share)		$ 1.84	$ 0.44
Number of options vested (in shares)		423,719	533,348
Weighted average fair value of options vested on grant date		$ 475,123	$ 549,453
Inducement options
Stock Options Outstanding
Options granted (in shares)		209,531
Ending balance (in shares)		209,531
Options vested, exercisable and expected to vest
Weighted average grant date fair value of stock options granted (in dollars per share)		$ 1.34
Number of options vested (in shares)		0
Common Stock
Options vested, exercisable and expected to vest
Share Price					$ 0.87
2013 Plan
Stock Incentive Plans
Option shares outstanding		33,769
2013 Plan | Stock options
Stock Options Outstanding
Options granted (in shares)		0
Ending balance (in shares)		33,769
2014 Plan
Stock Incentive Plans
Option shares outstanding		2,835,099
Shares Available for Grant
Beginning balance (in shares)		3,619
Additional shares authorized (in shares)		2,877,766
Options granted (in shares)		(2,767,673)
Options cancelled (in shares)		124,460
Ending balance (in shares)		238,172		3,619
Stock Options Outstanding
Beginning balance (in shares)		229,575
Options granted (in shares)		2,767,673
Options cancelled (in shares)		(128,380)
Ending balance (in shares)		2,868,868		229,575
RSUs Outstanding
Beginning balance (in shares)		392,904
Ending balance (in shares)		392,904		392,904
Weighted Average Stock Option Exercise Price
Beginning balance (in dollars per share)		$ 28.05
Ending balance (in dollars per share)		$ 5.96		$ 28.05
Weighted Average Remaining Contractual Life (Years)
Weighted Average Remaining Contractual Life (Years)		9 years 3 months 7 days		8 years 3 months 22 days
Options vested, exercisable and expected to vest
Options vested and exercisable (in shares)		709,721
Options vested and exercisable (in dollars per share)		$ 12.14
Options vested and exercisable (in years)		3 years 11 months 23 days
Options vested and expected to vest (in shares)		2,644,568
Options vested and expected to vest (in dollars per share)		$ 6.03
Options vested and expected to vest (in years)		9 years 3 months 4 days
Options exercised (in shares)		0	0
2014 Plan | Stock options
Stock Incentive Plans
Increase in share reserve based on outstanding number of shares (as a percent)	2.00%