Business Combinations - Summary of Estimated Fair Values of Assets Acquired and Liabilities Assumed (Details) - USD ($) $ in Thousands	Jun. 26, 2020	Mar. 06, 2020	Sep. 27, 2019	Jun. 12, 2019
Assets
Goodwill	$ 5,616,849		$ 5,432,544
Wood Group
Assets
Cash and cash equivalents		$ 24,300
Receivables		75,900
Other current assets		5,200
Property, equipment and improvements, net		8,300
Goodwill		205,800
Identifiable intangible assets		80,000
Miscellaneous		19,400
Total Assets		418,900
Liabilities
Accounts payable, accrued expenses and other current liabilities		71,800
Long term liabilities		29,200
Total Liabilities		101,000
Net assets acquired		$ 317,900
KeyW
Assets
Cash and cash equivalents				$ 29,100
Receivables				79,100
Inventories, net				19,300
Prepaid expenses and other				2,400
Property, equipment and improvements, net				24,500
Deferred tax asset and other				37,800
Goodwill				615,600
Identifiable intangible assets				179,000
Total Assets				986,800
Liabilities
Accounts payable, accrued expenses and other current liabilities				8,300
Accrued expenses				69,100
Short term debt				298,400
Other current liabilities				3,900
Other non-current liabilities				2,900
Total Liabilities				382,600
Net assets acquired				$ 604,200