Mergers and Acquisitions - GenVec - Fair Value of Assets Acquired and Liabilities Assumed (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jun. 30, 2017
Business Acquisition [Line Items]
Goodwill	$ 63,754	$ 93,627	$ 93,751
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 noncurrent 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