Mergers and Acquisitions - GenVec - Fair Value of Assets Acquired and Liabilities Assumed (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Business Acquisition [Line Items]
Goodwill	$ 164,931	$ 157,175
GenVec, Inc.
Business Acquisition [Line Items]
Cash and cash equivalents	2,054
Short term investments	542
Trade receivables	75
Other receivables	97
Prepaid expenses and other	227
Property and equipment	250
Intangible assets	14,000
Other non-current assets	58
Total assets acquired	17,303
Accounts payable	2,158
Accrued compensation and benefits	1,226
Other accrued expenses	856
Other long term liabilities	92
Deferred tax liabilities	239
Total liabilities assumed	4,571
Net assets acquired	12,732
Goodwill	4,850
Total consideration	$ 17,582