Income Taxes - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2013
Operating Loss Carryforwards [Line Items]
Federal corporate income tax rate	34.00%	34.00%	34.00%
Federal and state research and development tax credits	$ 11,385	$ 10,396
Retained earnings (accumulated deficit)	(847,820)	(729,341)
Estimated tax benefit upon enactment of Tax Act	2,185
Change in deferred tax assets resulting from enactment of Tax Act	87,473
Estimated tax benefit due to changes in deferred tax liabilities upon enactment of Tax Act	1,730
Estimated current tax benefit upon enactment of Tax Act	455
Provisional transition tax amount	0
Additional deferred tax liabilities recorded due to enacted foreign tax changes	15,620	$ 17,007
AquaBounty Technologies, Inc.
Operating Loss Carryforwards [Line Items]
Annual usage limit of operating loss carryforwards	$ 900
Expiration date of Federal income tax loss carryforwards	2018
Ownership percentage in AquaBounty (more than)				50.00%
Foreign Subsidiaries
Operating Loss Carryforwards [Line Items]
Retained earnings (accumulated deficit)	$ 65,052
Domestic
Operating Loss Carryforwards [Line Items]
Net operating losses inherited via acquisition	33,590
Operating loss carryforwards	244,274
Federal and state research and development tax credits	$ 7,737
Expiration date of Federal income tax loss carryforwards	2022
Domestic | GenVec, Inc.
Operating Loss Carryforwards [Line Items]
Net operating losses inherited via acquisition	$ 13,376
Domestic | AquaBounty Technologies, Inc.
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	28,209
Foreign
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	151,423
Foreign | AquaBounty Technologies, Inc.
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	15,653
Tax credit	2,832
BELGIUM
Operating Loss Carryforwards [Line Items]
Additional deferred tax liabilities recorded due to enacted foreign tax changes	$ 2,307