Related Party Transactions (Details)	1 Months Ended				3 Months Ended		6 Months Ended
	Sep. 30, 2019 ft²	Feb. 28, 2019 ft²	Dec. 31, 2018 ft²	Aug. 31, 2018 USD ($)	Jun. 30, 2020 USD ($) board_member shares	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($) board_member shares	Jun. 30, 2019 USD ($)	Dec. 31, 2019 USD ($) shares
Related Party Transaction [Line Items]
Common stock, shares outstanding (in shares) | shares					139,233,450		139,233,450		124,267,358
Operating lease right-of-use asset					$ 42,432,000		$ 42,432,000		$ 44,495,000	[1]
Operating lease liability					$ 53,462,000		$ 53,462,000		53,028,000
Pfizer
Related Party Transaction [Line Items]
Common stock, shares outstanding (in shares) | shares					22,032,040		22,032,040
Pfizer | Accrued and Other Current Liabilities
Related Party Transaction [Line Items]
Payable to related party, current					$ 0		$ 0		1,700,000
Pfizer | Transition Services Agreement
Related Party Transaction [Line Items]
Related party costs					0	$ 1,800,000	0	$ 4,200,000
Pfizer | Transition Services Agreement | Research and development
Related Party Transaction [Line Items]
Related party transaction, expenses from transactions with related party					0	400,000	0	1,000,000.0
Bellco | Sublease Agreement
Related Party Transaction [Line Items]
Area of office space (in square feet) | ft²			1,293
Sublease, term of contract (in years)			3 years
Operating lease right-of-use asset					100,000		100,000		100,000
Operating lease liability					100,000		100,000		$ 200,000
Bellco | Consulting Agreements
Related Party Transaction [Line Items]
Related party costs					$ 200,000	100,000	$ 400,000	300,000
Bellco | Consulting Agreements | Payments Commencing January 2019
Related Party Transaction [Line Items]
Related party transaction monthly payment in arrears				$ 33,333
Bellco | Consulting Agreements | Payments Commencing January 2020
Related Party Transaction [Line Items]
Related party transaction monthly payment in arrears				$ 37,500
Bellco | Consulting Agreements | Maximum
Related Party Transaction [Line Items]
Related party transaction compensation percentage				60.00%
ByHeart
Related Party Transaction [Line Items]
Number of members appointed to board of directors | board_member					2		2
ByHeart | Sublease Agreement
Related Party Transaction [Line Items]
Area of office space (in square feet) | ft²	2,907	2,180
Sublease income					$ 100,000	100,000	$ 200,000	100,000
Two River | Consulting Agreements
Related Party Transaction [Line Items]
Related party costs					$ 100,000	$ 100,000	$ 200,000	$ 300,000

[1] The balance sheet as of December 31, 2019 is derived from the audited financial statements as of that date.