Stock-Based Compensation Plans - Additional Information (Details) $ / shares in Units, $ in Thousands, € in Millions			1 Months Ended		3 Months Ended		9 Months Ended
	Apr. 12, 2019 USD ($)	Apr. 12, 2019 EUR (€)	Jul. 31, 2019 shares	Apr. 30, 2019 shares	Sep. 30, 2020 USD ($) shares	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) numberOfStockOptionPrograms $ / shares shares	Sep. 30, 2019 USD ($)	Sep. 30, 2017 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of stock option programs | numberOfStockOptionPrograms							2
Expected dividend yield							0.00%
Total unrecognized compensation expense | $					$ 6,500		$ 6,500
Period over which compensation cost will be recognized (in years)							3 years 25 days
VSOP and VSOP SB
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense | $	$ 508					$ 508		$ 508
VSOP
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares authorized for grant under stock option programs (in shares)							31,593
VSOP SB
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares authorized for grant under stock option programs (in shares)							31,593
Percent of Company's total issued shared capital available for grant under stock option programs							0.50%
Executive Bonus Agreement
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	$ 6,000	€ 5.3
Stock issued (in shares)				460,336
2014 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for grant (in shares)					43,311		43,311
2017 Inducement Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for grant (in shares)									46,250
2019 Omnibus Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for grant (in shares)			1,500,000
Expected term of options (years)							5 years 11 months 4 days
Expected dividend yield							0.00%
Options granted in period, weighted-average grant date fair value (in USD per share) | $ / shares							$ 8.75
2019 Omnibus Equity Incentive Plan, Evergreen Provision
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Additional shares authorized, percent			4.00%
Additional shares authorized (in shares)			4,900,000		448,634
Research and Development
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense | $								1,500
General and Administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense | $								$ 6,000
Incentive stock options | 2019 Omnibus Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period (in years)							4 years
Vital Therapies, Inc. | Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
RSUs granted (in shares)							127,500
Minimum | Non-statutory options | 2019 Omnibus Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period (in years)							3 years
Maximum | 2019 Omnibus Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term of options (years)							10 years
Maximum | Non-statutory options | 2019 Omnibus Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period (in years)							4 years