Assets and Liabilities Measured at Fair Value (Tables)

6 Months Ended

Jun. 30, 2020

Fair Value Disclosures [Abstract]

Summary of assets and liabilities subject to fair value measurements

A summary of the fair value of the Company's recurring assets and liabilities aggregated by the level in the fair value hierarchy within which those measurements fall as of June 30, 2020 are identified in the following table:

(in thousands)	Level 2		Total
Assets:
Commercial paper	$	59,902	$	59,902
Asset-backed securities	33,182		33,182
Corporate debt securities	51,532		51,532
Money market funds	3,635		3,635
	$	148,251	$	148,251

(in thousands)	Level 2		Level 3		Total
Liabilities:
Contingent consideration payable	$	—	$	24,327	$	24,327
Deferred compensation plan liability	3,312		—		3,312
	$	3,312	$	24,327	$	27,639

A summary of the fair value of the Company's recurring assets and liabilities aggregated by the level in the fair value hierarchy within which those measurements fall as of December 31, 2019 are identified in the following table:

(in thousands)	Level 2		Total
Assets:
Commercial paper	$	73,710	$	73,710
Asset-backed securities	77,810		77,810
Corporate debt securities	145,991		145,991
U.S. government agency bonds	11,991		11,991
Money market funds	4,768		4,768
	$	314,270	$	314,270

(in thousands)	Level 2		Level 3		Total
Liabilities:
Contingent consideration payable	$	—	$	22,681	$	22,681
Deferred compensation plan liability	4,419		—		4,419
	$	4,419	$	22,681	$	27,100

Schedule of significant unobservable inputs used in the valuation of the contingent consideration payable

The following significant unobservable inputs were used in the valuation of the contingent consideration payable of Callidus for the ATB-200 Pompe program:

Contingent Consideration Liability	Fair Value as of June 30, 2020		Valuation Technique	Unobservable Input	Range
	(in thousands)
				Discount rate	8.9%
Clinical and regulatory milestones	$	23,673	Probability weighted discounted cash flow	Probability of achievement of milestones	75% - 78%
				Projected year of payments	2021 - 2022

Schedule of changes in contingent consideration payable

The following table shows the change in the balance of contingent consideration payable for the three and six months ended June 30, 2020 and June 30, 2019, respectively:

	Three Months Ended June 30,				Six Months Ended June 30,
(in thousands)	2020		2019		2020		2019
Balance, beginning of the period	$	23,612	$	20,767	$	22,681	$	19,700
Changes in fair value during the period, included in the Consolidated Statements of Operations	715		480		1,646		1,863
Adjustment for contingent consideration paid in stock	—		—		—		(316)
Balance, end of the period	$	24,327	$	21,247	$	24,327	$	21,247