Agreements - Takeda (Details)	1 Months Ended		3 Months Ended														6 Months Ended		12 Months Ended
	Mar. 31, 2018 USD ($)	Mar. 31, 2015 USD ($) item	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Sep. 30, 2015 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2018 USD ($) item	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Jun. 30, 2016 USD ($)	May 31, 2018 USD ($)	Jan. 02, 2018 USD ($)
Collaborative Agreements disclosures
Revenue from contract with customer			$ 13,416,000	$ 10,928,000	$ 9,287,000	$ 19,815,000	$ 39,448,000	$ 8,480,000	$ 39,020,000	$ 28,499,000	$ 13,846,000	$ 7,660,000	$ 7,408,000	$ 19,714,000	$ 18,029,000	$ 14,851,000	$ 21,506,000	$ 32,880,000	$ 53,446,000	$ 115,447,000	$ 48,628,000	$ 60,002,000
Takeda
Collaborative Agreements disclosures
Term of agreement		3 years
Number of single-target licenses | item																			1
Term of extension of the agreement		1 year
Potential milestone payment		$ 210,000,000
Estimated term of development and commercialization license		25 years
Costs of services and materials																	0					0
Takeda | Maximum
Collaborative Agreements disclosures
Number of single-target licenses | item		2
Takeda | Development milestones
Collaborative Agreements disclosures
Potential milestone payment		$ 30,000,000
Takeda | Phase 2 clinical trial
Collaborative Agreements disclosures
Potential milestone payment			10,000,000																$ 10,000,000
Takeda | Regulatory milestones
Collaborative Agreements disclosures
Potential milestone payment		85,000,000
Takeda | Milestone payments
Collaborative Agreements disclosures
Potential milestone payment		95,000,000
Takeda | Technological Improvements
Collaborative Agreements disclosures
Potential milestone payment																								$ 400,000
Takeda | Right-to-test agreement
Collaborative Agreements disclosures
Potential milestone payment		4,000,000
Takeda | Option to expand scope of right-to-test
Collaborative Agreements disclosures
Potential milestone payment		8,000,000
ASU 2014-09 | Adjustments due to new guidance
Collaborative Agreements disclosures
Revenue from contract with customer																			5,000,000
ASU 2014-09 | Adjustments due to new guidance | Takeda | Phase 1 clinical trial
Collaborative Agreements disclosures
Potential milestone payment							5,000,000													5,000,000			$ 5,000,000
License and milestone fees
Collaborative Agreements disclosures
Revenue from contract with customer			1,747,000	672,000	1,321,000	11,540,000	29,580,000	79,000	31,080,000	18,730,000	5,076,000	76,000	76,000	10,077,000	10,692,000	6,070,000	5,152,000	16,762,000	15,280,000	79,469,000	15,305,000	26,915,000
License and milestone fees | Takeda
Collaborative Agreements disclosures
Revenue from contract with customer	$ 10,900,000																					8,600,000
Potential milestone payment		210,000,000
License and milestone fees | ASU 2014-09 | Adjustments due to new guidance
Collaborative Agreements disclosures
Potential milestone payment			5,000,000																5,000,000
Upfront payment | Takeda
Collaborative Agreements disclosures
Revenue from contract with customer		$ 20,000,000
Research and development support
Collaborative Agreements disclosures
Revenue from contract with customer			218,000	388,000	388,000	383,000	452,000	650,000	902,000	1,478,000	1,427,000	1,354,000	1,335,000	1,059,000	848,000	772,000	2,781,000	1,620,000	1,377,000	3,482,000	5,175,000	4,014,000
Costs of services and materials																	22,000
Research and development support | Takeda
Collaborative Agreements disclosures
Costs of services and materials																	678,000		199,000	913,000		469,000
Clinical materials revenue
Collaborative Agreements disclosures
Revenue from contract with customer			$ 2,170,000	$ 1,427,000	$ 336,000	$ 702,000	$ 1,829,000	$ 1,248,000	$ 599,000	$ 678,000	$ 633,000	$ 46,000	$ 53,000	$ 1,198,000	$ 3,000	$ 2,325,000	$ 679,000	$ 2,328,000	4,635,000	4,354,000	$ 1,930,000	$ 3,579,000
Clinical materials revenue | Takeda
Collaborative Agreements disclosures
Costs of services and materials																			$ 650,000,000,000	$ 2,100,000