Collaborative Arrangements - Textual (Details) - USD ($)	1 Months Ended								3 Months Ended		6 Months Ended		12 Months Ended
	May 31, 2019	Sep. 30, 2018	Apr. 30, 2018	Oct. 31, 2017	Mar. 31, 2017	Dec. 31, 2016	Aug. 31, 2015	Feb. 29, 2012	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2017	Dec. 31, 2018
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Total revenues									$ 12,319,000	$ 13,538,000	$ 27,901,000	$ 27,580,000
Contract with customer, liability									9,100,000		9,100,000			$ 8,288,000
Deferred revenue									5,851,000		5,851,000			4,936,000
Research and Development Revenue [Member]
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Total revenues									6,070,000	9,815,000	13,665,000	17,694,000
Merck [Member] | Product [Member]
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Total revenues									2,500,000	2,700,000	7,800,000	7,200,000
Merck [Member] | Collaborative Arrangement [Member] | Research and Development Revenue [Member]
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Total revenues									1,000,000.0	1,000,000.0	2,000,000.0	1,900,000
Nestec Ltd. (Nestle Health Sciences) [Member] | Global Development, Option and License Agreement [Member]
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Milestone revenue				$ 14,000,000.0
Contract with customer, liability									200,000		200,000			1,900,000
Research and development revenue									500,000	1,800,000	1,700,000	4,500,000
Nestec Ltd. (Nestle Health Sciences) [Member] | Global Development, Option and License Agreement [Member] | Milestone One [Member]
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Progress payment amount				4,000,000.0
Nestec Ltd. (Nestle Health Sciences) [Member] | Global Development, Option and License Agreement [Member] | Milestone Two [Member]
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Progress payment amount				1,000,000.0
Nestec Ltd. (Nestle Health Sciences) [Member] | CDX-6114 [Member]
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Cumulative catch-up adjustment to revenue, change in measure of progress											3,000,000.0
Nestec Ltd. (Nestle Health Sciences) [Member] | Collaborative Arrangement [Member] | Strategic Collaboration Agreement [Member]
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Milestone revenue		$ 600,000
Research and development revenue									1,200,000	600,000	2,500,000	1,200,000	$ 1,200,000
Deferred revenue									300,000		300,000			800,000
Porton [Member] | Porton Agreement [Member]
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Milestone revenue			$ 500,000
Number of days for payment			30 days
Technology Transfer, Collaboration and License Agreement [Member] | Merck [Member]
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
License revenue, contingent receivables							$ 15,000,000.0
Technology Transfer, Collaboration and License Agreement [Member] | Minimum [Member]
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
License revenue, contingent receivables											5,750,000
Technology Transfer, Collaboration and License Agreement [Member] | Maximum [Member]
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
License revenue, contingent receivables											38,500,000
Merck Platform Technology Transfer and License Agreement, Protein Engineering [Member] | Merck [Member] | Collaborative Arrangement [Member] | Research and Development Revenue [Member]
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Total revenues									900,000		900,000
Supply Agreement [Member] | Merck [Member]
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Term of collaborative research and development agreement								5 years
Optional extension period								5 years
Contract with customer, liability									1,500,000		1,500,000			3,600,000
Supply Agreement [Member] | Merck [Member] | Research and Development Revenue [Member]
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Total revenues									0	0	0	1,300,000
Supply Agreement [Member] | Customer [Member]
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Milestone revenue						$ 800,000
Contract with customer, liability									2,000,000.0		2,000,000.0			2,000,000
Research and Development Agreement [Member] | Fine chemical customer [Member]
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Term of collaborative research and development agreement					21 months
Milestone revenue					$ 3,000,000.0
Contract with customer, liability									0		0			$ 0
Research and development revenue										$ 4,500,000		$ 5,900,000
Research and Development Agreement [Member] | Maximum [Member] | Nestec Ltd. (Nestle Health Sciences) [Member] | Global Development, Option and License Agreement [Member]
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Milestone revenue				85,000,000.0
Sales-Based Milestone [Member] | Nestec Ltd. (Nestle Health Sciences) [Member] | Global Development, Option and License Agreement [Member]
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Target sales for sales milestone				1,000,000,000.0
Sales-Based Milestone [Member] | Maximum [Member] | Nestec Ltd. (Nestle Health Sciences) [Member] | Global Development, Option and License Agreement [Member]
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Milestone revenue				$ 250,000,000.0
Platform Technology Transfer and License Agreement [Member] | Novartis [Member]
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Term of collaborative research and development agreement	20 months
Milestone revenue	$ 5,000,000
Contract with customer, liability									5,000,000.0		5,000,000.0
Research and development revenue									$ 0		$ 0
Contingent annual receivable increase	8,000,000
Platform Technology Transfer and License Agreement, Milestone One [Member] | Novartis [Member]
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Contingent receivable	4,000,000
Platform Technology Transfer and License Agreement, Milestone Two [Member] | Novartis [Member]
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Contingent receivable	$ 5,000,000