Collaborative Arrangements - Textual (Details) - USD ($)	1 Months Ended							3 Months Ended		9 Months Ended
	Sep. 30, 2018	Apr. 30, 2018	Oct. 31, 2017	Mar. 31, 2017	Dec. 31, 2016	Aug. 31, 2015	Feb. 29, 2012	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Jan. 01, 2018	Dec. 31, 2017
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total revenues								$ 16,946,000	$ 9,984,000	$ 44,526,000	$ 28,301,000
Contract with customer, liability	$ 8,684,000							8,684,000		8,684,000		$ 18,966,000	$ 18,966,000
Deferred revenue	4,253,000							4,253,000		4,253,000			12,292,000
Revenue recognized								16,946,000		44,526,000
Research and Development Revenue [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total revenues								8,541,000	3,036,000	26,235,000	9,167,000
Merck [Member] | Product [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total revenues								3,400,000	1,500,000	10,700,000	6,500,000
Nestec Ltd. (Nestle Health Sciences) [Member] | Global Development, Option and License Agreement [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone revenue			$ 14,000,000
Contract with customer, liability	0							0		0			6,800,000
Research and development revenue								2,300,000	0	6,800,000	0
Revenue recognized								1,300,000	0	1,300,000	0
Progress payment amount										4,000,000
Event of counterparty exercising alternative option										$ 3,000,000
Duration to pay after license effective date										60 days
Nestec Ltd. (Nestle Health Sciences) [Member] | Global Development, Option and License Agreement [Member] | Transferred over Time [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contract with customer, liability	2,700,000							2,700,000		$ 2,700,000			0
Nestec Ltd. (Nestle Health Sciences) [Member] | Strategic Collaboration Agreement [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone revenue	600,000
Porton [Member] | Porton Agreement [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone revenue		$ 500,000
Number of days for payment		30 days
Contract with customer, liability	500,000							500,000		500,000			0
Research and development revenue								0	0	0	0
Collaborative Arrangement [Member] | Merck [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Proceeds from license fees received						$ 5,000,000
Collaborative Arrangement [Member] | Merck [Member] | Research and Development Revenue [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total revenues								1,100,000	900,000	3,000,000	2,700,000
Collaborative Arrangement [Member] | Nestec Ltd. (Nestle Health Sciences) [Member] | Strategic Collaboration Agreement [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Research and development revenue								1,200,000	0	2,400,000	0
Deferred revenue	1,100,000							1,100,000		1,100,000			1,100,000
Technology Transfer, Collaboration and License Agreement [Member] | Merck [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Maximum milestone receivable						$ 15,000,000
Supply Agreement [Member] | Merck [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Term of collaborative research and development agreement							5 years
Optional extension period							5 years
Contract with customer, liability	4,500,000							4,500,000		4,500,000			1,500,000
Supply Agreement [Member] | Merck [Member] | Research and Development Revenue [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total revenues								0	300,000	1,300,000	1,000,000
Supply Agreement [Member] | Customer [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone revenue					$ 800,000
Contract with customer, liability	2,000,000							2,000,000		2,000,000			700,000
Research and Development Agreement [Member] | Fine chemical customer [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Term of collaborative research and development agreement				21 months
Milestone revenue				$ 3,000,000
Contract with customer, liability	0							0		0			$ 3,100,000
Research and development revenue								1,300,000	$ 1,100,000	7,100,000	$ 1,900,000
Sales-Based Milestone [Member] | Nestec Ltd. (Nestle Health Sciences) [Member] | Global Development, Option and License Agreement [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Target sales for sales milestone			1,000,000,000
Minimum [Member] | Technology Transfer, Collaboration and License Agreement [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
License revenue, contingent receivables	5,750,000							5,750,000		5,750,000
Maximum [Member] | Technology Transfer, Collaboration and License Agreement [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
License revenue, contingent receivables	$ 38,500,000							$ 38,500,000		$ 38,500,000
Maximum [Member] | Research and Development Agreement [Member] | Nestec Ltd. (Nestle Health Sciences) [Member] | Global Development, Option and License Agreement [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone revenue			86,000,000
Maximum [Member] | Sales-Based Milestone [Member] | Nestec Ltd. (Nestle Health Sciences) [Member] | Global Development, Option and License Agreement [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone revenue			$ 250,000,000