Accounts Receivable, Net and Supplemental Balance Sheet Information (Tables)

12 Months Ended

Dec. 31, 2018

Accounts Receivable, Net and Supplemental Balance Sheet Information [Abstract]

Schedule of accounts receivable [Table Text Block]

Accounts receivable, net, consisted of the following:

	December 31,
	2018		2017
Accounts receivable	$	158,556	$	143,244
Unbilled receivables	40,671		29,895
	199,227		173,139
Less allowances for doubtful accounts	3,321		4,468
	$	195,906	$	168,671

Schedule of other current assets [Table Text Block]

The following items comprise the amounts included in the balance sheets:

	December 31,
Other current assets	2018		2017
Refundable income taxes	$	1,625	$	587
Other	932		784
Total	$	2,557	$	1,371

Schedule of other assets, noncurrent [Table Text Block]

	December 31,
Other assets, noncurrent	2018		2017
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
Total	$	21,769	$	29,156

Schedule of accrued expenses [Table Text Block]

	December 31,
Accrued expenses	2018		2017
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
Total	$	44,061	$	42,816

Schedule of other liabilities, noncurrent [Table Text Block]

	December 31,
Other liabilities, noncurrent	2018		2017
Pension and retirement plans	$	6,138	$	14,759
Other	3,987		5,207
Total	$	10,125	$	19,966