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Stock Compensation Plan (Tables)
 12 Months Ended
Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Schedule of Nonvested Restricted Stock Units Activity [Table Text Block]
Restricted stock unit ("RSU") awards for the year ended December 31, 2019 were as follows:
 
Units
Unvested balance - January 1, 2019
0
Granted
125,000
Unvested balance - December 31, 2019
125,000
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Table Text Block]
The following table summarizes the reporting of total stock-based compensation expense resulting from stock options, restricted stock units and the employee stock purchase plan (in thousands):
 
Years Ended December 31,
 
2019
 
2018
 
 
Research and development
$
1,168

 
$
518

Selling, general and administrative
5,316

 
1,210

     Total stock-based compensation expense
$
6,484

 
$
1,728
Share-based Payment Arrangement, Option [Member]  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Stock-based Compensation Assumptions Used in Black-Scholes Option Valuation Model
The fair value of stock options granted was estimated with the following weighted average assumptions:
 
Years Ended December 31,
 
2019
 
2018
Expected term (years)
6.0

 
6.0

Risk-free interest rate
2.14
%
 
2.48
%
Expected volatility
60.27
%
 
56.84
%
Expected dividends
—

 
—
Share-based Compensation, Activity
Stock option activity under the 2011 Plan, 2018 Plan and Inducement Plan for the year ended December 31, 2019 was as follows:
 
OPTIONS 
 
WEIGHTED
AVERAGE
EXERCISE PRICE  
 
WEIGHTED
AVERAGE CONTRACTUAL 
LIFE (YEARS)  
Outstanding - January 1, 2019
3,130,700
 
$
8.06

 
8.69
Granted
1,600,650
 
12.21

 
  
Exercised and vested
(128,307)
 
1.99

 
 
Forfeited
(172,655)
 
16.33

 
 
Expired
(1,403)
 
19.77

 
 
Outstanding - December 31, 2019
4,428,985
 
$
9.40

 
8.19
Exercisable - December 31, 2019
1,647,911
 
$
6.07

 
7.31
Vested and expected to vest at December 31, 2019
4,202,205
 
$
9.32

 
8.16

The weighted average fair value of awards granted during the year ended December 31, 2019 was $6.97 per share. The total intrinsic value of options exercised during the year ended December 31, 2019 was $1.0 million. The aggregate intrinsic value of awards vested and expected to vest as of December 31, 2019 was $7.8 million.

Restricted stock units  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block]
The fair value of the ESPP Plan shares was estimated using the Black-Scholes option-pricing model with the following weighted-average assumptions:
 
Year Ended December 31, 2019
Expected term (years)
0.5
Risk-free interest rate
1.85%
Expected volatility
70.70%
Expected dividends
—