Collaborative and Other Agreements (Narrative) (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2013
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Licensing payments received	$ 22,000	$ 29,000	$ 103,000	$ 106,000	$ 128,000	$ 143,000	$ 102,000	$ 102,000	$ 260,000	$ 475,000
Intrexon Corporation [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Value of common stock paid for technology access fee											$ 3,000,000
Fees payable upon commencement of the first Phase 2 trial	2,500,000								2,500,000
Fees payable upon first regulatory approval	$ 5,000,000								5,000,000
Milestone payments paid per collaboration agreement									0
Expenses incurred under Channel Collaboration Agreement									61,000	178,000
Cash paid for channel collaboration agreement									117,000	125,000
University Of Leicester [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Expenses incurred under Channel Collaboration Agreement									166,000	265,000
Cash paid for channel collaboration agreement									202,000	290,000
University Of Glasgow [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Expenses incurred under Channel Collaboration Agreement									0	61,000
Cash paid for channel collaboration agreement									0	61,000
Walter Reed Army Institute Of Research [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Payments for services under collaborative agreement									$ 0	0
Takara Bio Inc [Member] | Nonsoftware License Arrangement [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Licensing payments received						$ 40,000
Percent of license product sales receivable									12.00%
Percent of license product service revenues receivable									6.00%
Minimum annual royalty payments receivable									$ 15,000
Patent license agreement revenue									15,000	$ 0
Takara Bio Inc [Member] | Nonsoftware License Arrangement [Member] | Criteria One [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contingent licensing receivable									30,000
Licensed product revenues milestone benchmark									1,000,000
Takara Bio Inc [Member] | Nonsoftware License Arrangement [Member] | Criteria Two [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contingent licensing receivable									40,000
Licensed product net sales milestone benchmark									$ 2,000,000
Common Stock [Member] | Intrexon Corporation [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Value of common stock paid for technology access fee											$ 3,000,000