Mergers and Acquisitions - GenVec - Fair Value of Assets Acquired and Liabilities Assumed (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Jun. 30, 2017
Business Acquisition [Line Items]
Goodwill	$ 154,748	$ 153,289
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