Stock-Based Compensation Plans - Additional Information (Details) $ / shares in Units, $ in Thousands, € in Millions				1 Months Ended		3 Months Ended	6 Months Ended
	Apr. 12, 2019 USD ($)	Apr. 12, 2019 EUR (€)	Apr. 16, 2018 shares	Jul. 31, 2019 shares	Apr. 30, 2019 shares	Jun. 30, 2020 USD ($) shares	Jun. 30, 2020 USD ($) $ / shares shares	Jun. 30, 2019 USD ($)	Sep. 30, 2018 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense | $							$ 1,500
Total unrecognized compensation expense | $						$ 2,100	$ 2,100
Period over which compensation cost will be recognized, in years							2 years 9 months 14 days
VSOP and VSOP SB
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense | $	$ 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
Shares of common stock for annual increase in shares available for issuance (in shares)			1,200,000
Percent of outstanding stock for annual increase in shares available for issuance			3.00%
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
Options granted in period, weighted-average grant date fair value (in USD per share) | $ / shares							$ 5.86
Expected term of options (years)							5 years 9 months 3 days
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
Incentive stock options | 2014 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period (in years)							4 years
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 | 2014 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period (in years)							3 years
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 | 2014 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term of options (years)							10 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 | 2014 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period (in years)							4 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