Collaborative Arrangements (Details) - USD ($)	1 Months Ended											12 Months Ended
	Feb. 28, 2019	Jan. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Apr. 30, 2018	Oct. 31, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Aug. 31, 2015	Feb. 29, 2012	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2018
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Sales revenue, goods												$ 60,594,000	$ 50,024,000	$ 48,837,000
Contract with customer, liability			$ 8,288,000									8,288,000			$ 18,966,000
Deferred revenue - current			4,936,000									4,936,000	12,292,000
Liability, revenue recognized												60,594,000
Research and Development Revenues
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Sales revenue, goods												35,004,000	23,339,000
Supply Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront milestone payment									$ 800,000
Supply Agreement | Merck
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Term of milestone agreement											5 years
Term of agreement extension											5 years
Supply Agreement | License and Service | Merck
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Sales revenue, goods							$ 300,000					1,300,000	1,300,000	1,300,000
GSK Platform | Minimum | Technology Transfer and License Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contingent receivables				$ 5,750,000
GSK Platform | Maximum | Technology Transfer and License Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contingent receivables				38,500,000
Merck
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Sales revenue, goods												12,300,000	9,000,000	5,900,000
Merck | Collaborative Arrangement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Proceeds from license fees received										$ 5,000,000
Merck | Collaborative Arrangement | Research and Development Revenues
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Sales revenue, goods												4,100,000	3,600,000	$ 3,000,000
Merck | Technology Transfer and License Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Maximum milestone receivable										$ 15,000,000
Merck | Supply Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contract with customer, liability			3,600,000									3,600,000	1,500,000
Customer | Supply Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contract with customer, liability			2,000,000									2,000,000	700,000
Fine Chemical Customer | Research and Development Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contract with customer, liability			0									0	3,100,000
Upfront milestone payment								$ 3,000,000
Term of collaborative research and development agreement								21 months
Research and development revenues												7,100,000	3,200,000
Nestec Ltd. (Nestle Health Sciences) | CDX-6114 | Subsequent Event
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Progress payment eligible after commencement of Phase 1a clinical trial		$ 3,000,000
Nestec Ltd. (Nestle Health Sciences) | Collaborative Arrangement | Global Development, Option and License Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront milestone payment						$ 14,000,000
Research and development revenues												9,900,000	7,200,000
Progress payment eligible after commencement of Phase 1a clinical trial				4,000,000									$ 4,000,000
Duration to pay after license effective date													60 days
Nestec Ltd. (Nestle Health Sciences) | Collaborative Arrangement | Global Development, Option and License Agreement | Transferred over Time
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contract with customer, liability			1,900,000									1,900,000	$ 6,800,000
Nestec Ltd. (Nestle Health Sciences) | Collaborative Arrangement | CDX-6114
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payment amount			$ 1,000,000
Duration to pay after milestone achievement			60 days
Nestec Ltd. (Nestle Health Sciences) | Collaborative Arrangement | CDX-6114 | Subsequent Event
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Duration to pay after license effective date	60 days
Amount from exercising alternative option	$ 3,000,000
Threshold to achieve aggregate milestone amount	1,000,000,000
Nestec Ltd. (Nestle Health Sciences) | Collaborative Arrangement | Strategic Collaboration Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront milestone payment				$ 600,000
Research and development revenues													1,200,000
Deferred revenue - current			$ 800,000									800,000	1,100,000
Liability, revenue recognized												3,600,000	$ 500,000
Nestec Ltd. (Nestle Health Sciences) | Development and Approval | Collaborative Arrangement | CDX-6114 | Subsequent Event
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Maximum milestone receivable	86,000,000
Nestec Ltd. (Nestle Health Sciences) | Sales-based Milestone | Collaborative Arrangement | CDX-6114 | Subsequent Event
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Maximum milestone receivable	$ 250,000,000
Porton | Porton Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront milestone payment					$ 500,000
Research and development revenues												$ 2,800,000
Number of days for payment					30 days