Business Combinations - Summary of Estimated Fair Values of Assets Acquired and Liabilities Assumed (Details) - USD ($) $ in Thousands	Mar. 29, 2019	Sep. 28, 2018	Dec. 15, 2017
Assets
Goodwill	$ 4,774,849	$ 4,795,856
CH2M HILL Companies, Ltd.
Assets
Cash and cash equivalents			$ 315,200
Receivables			1,120,600
Prepaid expenses and other			72,700
Property, equipment and improvements, net			175,100
Goodwill			3,101,000
Identifiable intangible assets:
Total identifiable intangible assets			416,700
Miscellaneous			543,600
Total Assets			5,744,900
Liabilities
Notes payable			2,200
Accounts payable			309,600
Accrued liabilities			735,700
Billings in excess of costs			260,800
Identifiable intangible liabilities:
Lease intangible liabilities			9,600
Long-term debt			706,000
Other deferred liabilities			659,000
Total Liabilities			2,682,900
Noncontrolling interests			(37,300)
Net assets acquired			3,024,700
CH2M HILL Companies, Ltd. | Customer relationships, contracts and backlog
Identifiable intangible assets:
Total identifiable intangible assets			412,300
CH2M HILL Companies, Ltd. | Lease intangible assets
Identifiable intangible assets:
Total identifiable intangible assets			$ 4,400