Collaboration Agreements - Vertex – 2016 Strategic Alliance in Cystic Fibrosis (Details)	1 Months Ended		3 Months Ended								12 Months Ended
	Jul. 31, 2019 USD ($) extension_period	Jul. 31, 2016 USD ($)	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Jan. 01, 2019 USD ($)
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Transaction price			$ 249,500,000								$ 249,500,000
Deferred revenue			199,528,000				$ 240,924,000				199,528,000	$ 240,924,000
Collaboration revenue			14,055,000	$ 17,046,000	$ 13,083,000	$ 16,025,000	35,421,000	$ 41,757,000	$ 28,851,000	$ 29,039,000	60,209,000	135,068,000	$ 205,825,000
Revenue from contract with customer, excluding assessed tax											60,209,000
Collaboration revenue
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Collaboration revenue											42,803,000	76,519,000	146,953,000
Revenue from contract with customer, excluding assessed tax											42,803,000
Vertex Agreement
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Upfront cash payments		$ 20,000,000
Research period		3 years
Transaction price					4,100,000									$ 24,400,000
Deferred revenue			$ 800,000				$ 3,300,000				800,000	3,300,000
Research extension period	1 year
Proceeds from equity investment	$ 20,000,000
Termination period	90 days
Termination period upon marketing approval	180 days
Research extension period elected	6 months
Revenue from contract with customer, excluding assessed tax	$ 2,000,000
Research extension period	18 months
Number of extension periods | extension_period	2
Vertex Agreement | Collaboration revenue
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenue from contract with customer, excluding assessed tax											6,200,000	$ 10,400,000	$ 9,100,000
Vertex Agreement | Development Milestones
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Estimated arrangement consideration	$ 55,000,000.0
Vertex Agreement | Regulatory Milestones
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Estimated arrangement consideration	220,000,000.0
Vertex Agreement | Regulatory Milestones, Subsequent Products
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Estimated arrangement consideration	$ 3,000,000.0
Upfront Payment | Vertex Agreement
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Transaction price					2,000,000									20,000,000
Research And Development Funding | Vertex Agreement
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Transaction price					$ 2,100,000									$ 4,400,000
Change in estimation											$ 100,000