Accounts Receivable, Net and Supplemental Balance Sheet Information (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Accounts receivable, net
Accounts receivable	$ 158,556	$ 143,244
Unbilled receivables	40,671	29,895
Accounts receivable, gross, current	199,227	173,139
Less allowances for doubtful accounts	3,321	4,468
Accounts receivable, net	195,906	168,671
Other current assets
Refundable income taxes	1,625	587
Other	932	784
Other current assets, total	2,557	1,371
Other assets, noncurrent
Assets invested for self-insurance	15,379	19,422
Investment--cost-method affiliate	1,218	1,218
Deferred income taxes	573	4,815
Other	4,599	3,701
Other assets, noncurrent, total	21,769	29,156
Accrued expenses
Employee compensation	24,086	20,794
Accrued compensated absences	9,711	9,267
Self-insured medical claims	3,343	3,193
Customer advances, deposits	1,322	1,672
Income taxes payable	31	3,443
Taxes, other than income	2,546	2,279
Other	3,022	2,168
Accrued expenses, total	44,061	42,816
Other liabilities, noncurrent
Pension and retirement plans	6,138	14,759
Other	3,987	5,207
Other liabilities, noncurrent, total	$ 10,125	$ 19,966