Accounts Receivable, Net and Supplemental Balance-Sheet Information (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Accounts receivable, net
Accounts receivable	$ 135,920	$ 143,244
Receivables under contractual arrangements	46,613	29,895
Accounts receivable, gross	182,533	173,139
Less allowances for doubtful accounts	4,264	4,468
Accounts receivable, net	178,269	168,671
Other current assets
Refundable income taxes	0	587
Prepaid expense	11,938	15,893
Other	388	784
Total	12,326	17,264
Accrued expenses
Employee compensation	17,267	20,794
Accrued compensated absences	9,959	9,267
Self-insured medical claims	4,666	3,193
Income tax payable	2,610	3,443
Customer advances, deposits	498	1,672
Taxes, other than income	3,099	2,279
Other	2,413	2,168
Total	40,512	42,816
Other current liabilities
Note payable	0	149
Current portion of long-term debt	9,944	16,817
Current portion of self-insurance accruals	24,015	23,782
Total	$ 33,959	$ 40,748