CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash flows from operating activities:
Net income	$ 31,294	$ 21,154	$ 21,431
Adjustments to reconcile net income to net cash flows provided by (used in) operating activities –
Depreciation and amortization of property and equipment	38,070	38,077	38,236
Amortization of intangible assets	1,843	499	886
Stock-based compensation expense	3,165	4,376	4,674
Deferred income taxes	3,649	(5,091)	4,205
Gain on sale of property and equipment	(3,832)	(3,664)	(1,341)
Other non-cash items	237	1,194	194
Changes in operating assets and liabilities, net of acquisitions
Accounts receivable, net	(15,871)	(35,944)	(22,473)
Contract assets	(28,141)	(17,857)	(22,013)
Receivable for insurance claims in excess of deductibles	(9,229)	(39)	(7,187)
Other assets	2,280	(2,213)	3,730
Accounts payable	19,953	8,149	17,322
Contract liabilities	22,551	(14,317)	790
Accrued self-insurance	8,701	2,765	5,617
Other liabilities	10,119	(6,287)	10,419
Net cash flows provided by (used in) operating activities	84,789	(9,198)	54,490
Cash flows from investing activities:
Proceeds from sale of property and equipment	4,583	4,342	3,299
Cash paid for acquisitions, net of cash acquired	(47,082)	0	(12,056)
Purchases of property and equipment	(50,704)	(30,843)	(25,371)
Net cash flows used in investing activities	(93,203)	(26,501)	(34,128)
Cash flows from financing activities:
Net borrowings (repayments) under revolving lines of credit	(20,655)	19,890	59,070
Payment of principal obligations under capital leases	(1,081)	(1,203)	(740)
Borrowings under equipment notes	31,486	0	0
Proceeds from exercise of stock options	1,897	1,232	6,218
Repurchase of common shares	(1,043)	(3,058)	(101,483)
Other financing activities	38	28	1,396
Net cash flows provided by (used in) financing activities	10,642	16,889	(35,539)
Effect of exchange rate changes on cash	(64)	307	(774)
Net increase (decrease) in cash and cash equivalents	2,164	(18,503)	(15,951)
Cash and cash equivalents:
Beginning of period	5,343	23,846	39,797
End of period	7,507	5,343	23,846
Supplemental Cash Flow Information:
Income taxes payments	7,247	6,597	6,274
Interest payments	3,097	2,259	1,114
Noncash investing activities:
Acquisition of property and equipment for which payment is pending	953	2,050	614
Acquisition of property under capital lease arrangements	0	0	5,658
Noncash financing activities:
Capital lease obligations initiated	$ 0	$ 0	$ 5,658