Assets and Liabilities Measured at Fair Value - Significant Unobservable Inputs (Details) $ in Thousands	Sep. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Contingent consideration payable	$ 25,361	$ 22,681
Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Contingent consideration payable	25,361	$ 22,681
Callidus Biopharma Inc | Clinical and regulatory milestones | ATB200 Pompe Program
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Contingent consideration payable	$ 24,650
Callidus Biopharma Inc | Clinical and regulatory milestones | Probability of achievement of milestones | ATB200 Pompe Program | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Contingent consideration, measurement input	0.75
Callidus Biopharma Inc | Clinical and regulatory milestones | Probability of achievement of milestones | ATB200 Pompe Program | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Contingent consideration, measurement input	0.78
Callidus Biopharma Inc | Clinical and regulatory milestones | Level 3 | Discount rate | ATB200 Pompe Program | Probability weighted discounted cash flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Contingent consideration, measurement input	0.075