Quarterly Results (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 28, 2019	Sep. 28, 2019	Jun. 29, 2019	Mar. 30, 2019	Dec. 31, 2020	Dec. 28, 2019	Dec. 29, 2018
Selected Quarterly Financial Information [Line Items]
Revenue	$ 1,395,025	$ 1,368,673	$ 1,330,349	$ 1,411,741	$ 1,442,232	$ 1,429,428	$ 1,431,061	$ 1,389,877	$ 5,505,788	$ 5,692,598	$ 5,366,325
Earnings before income taxes	176,132	459,840	171,530	183,971	191,701	102,312	154,123	206,376	991,473	654,512	800,851
Net earnings	$ 141,505	$ 356,676	$ 134,748	$ 147,159	$ 154,331	$ 81,935	$ 126,969	$ 166,219	$ 780,088	$ 529,454	$ 630,059
Basic earnings per share	$ 0.46	$ 1.17	$ 0.44	$ 0.48	$ 0.49	$ 0.26	$ 0.40	$ 0.51	$ 2.54	$ 1.66	$ 1.91
Diluted earnings per share	$ 0.46	$ 1.16	$ 0.44	$ 0.47	$ 0.49	$ 0.26	$ 0.39	$ 0.51	$ 2.52	$ 1.65	$ 1.89
Quarterly Financial Information, Quarterly Charges and Credits, Amount Affecting Comparability	$ 4,000	$ 217,000
Employee Separation Costs [Member]
Selected Quarterly Financial Information [Line Items]
Quarterly Financial Information, Quarterly Charges and Credits, Amount Affecting Comparability					$ 13,000	$ 32,000	$ 41,000
Contract Termination [Member]
Selected Quarterly Financial Information [Line Items]
Quarterly Financial Information, Quarterly Charges and Credits, Amount Affecting Comparability					$ 6,000	$ 60,000