Accounts Receivable, Net and Supplemental Balance-Sheet Information (Details) - USD ($) $ in Thousands	Mar. 28, 2020	Dec. 31, 2019
Accounts receivable, net
Accounts receivable	$ 168,503	$ 176,849
Unbilled Receivables(1)	82,051	58,277
Accounts receivable, gross	250,554	235,126
Less allowances for doubtful accounts	2,887	3,815
Accounts receivable, net	247,667	231,311
Other current assets
Refundable income taxes	1,366	339
Prepaid expense	17,364	25,664
Other	793	984
Total	19,523	26,987
Property, Plant and Equipment, Net [Abstract]
Land and Land Improvements	19,106	19,270
Buildings and leasehold improvements	44,267	44,414
Equipment	613,398	604,211
Property, Plant and Equipment, Gross	676,771	667,895
Less accumulated depreciation	473,789	468,045
Property and equipment, net	202,982	199,850
Other Assets, Noncurrent [Abstract]
Assets invested for self-insurance	14,166	15,426
Investment--cost-method affiliate	1,314	1,314
Other	5,514	5,595
Total	20,994	22,335
Accrued expenses
Employee compensation	12,317	26,381
Accrued compensated absences	10,197	10,744
Self-insured medical claims	2,451	1,824
Income tax payable	5,590	6,420
Customer advances, deposits	85	1,674
Taxes, other than income	4,514	1,775
Other	3,077	3,613
Total	38,231	52,431
Other current liabilities
Notes payable	6,520	1,853
Current operating lease liabilities	16,920	14,665
Current portion of long-term debt	20,775	23,302
Self-insurance reserve	30,855	30,882
Total	54,295	47,400
Other noncurrent liabilities
Pension and retirement plans	6,804	6,552
Deferred income taxes	484	567
Other	5,107	5,149
Other noncurrent liabilities	$ 12,395	$ 12,268