CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash flows from operating activities:
Net income	$ 58,759	$ 36,214	$ 31,294
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation and amortization of property and equipment	42,867	40,667	38,070
Amortization of intangible assets	3,586	3,849	1,843
Stock-based compensation expense	5,688	4,403	3,165
Deferred income taxes	(2,641)	3,602	3,649
Gain on sale of property and equipment	(2,813)	(3,543)	(3,832)
Other non-cash items	1,951	1,029	237
Changes in operating assets and liabilities, net of acquisitions:
Accounts receivable, net	2,903	(39,710)	(15,871)
Contract assets	31,360	(16,443)	(28,141)
Receivable for insurance claims in excess of deductibles	(1,511)	(9,646)	(9,229)
Other assets	(15,458)	(10,327)	2,280
Accounts payable	(43,079)	22,492	19,953
Contract liabilities	52,918	28,163	22,551
Accrued self-insurance	3,010	12,755	8,701
Other liabilities	37,627	(8,606)	10,119
Net cash flows provided by operating activities	175,167	64,899	84,789
Cash flows from investing activities:
Proceeds from sale of property and equipment	3,429	4,051	4,583
Cash paid for acquisitions, net of cash acquired	0	(79,720)	(47,082)
Purchases of property and equipment	(44,355)	(57,828)	(50,704)
Net cash flows used in investing activities	(40,926)	(133,497)	(93,203)
Cash flows from financing activities:
Net borrowings (repayments) under revolving lines of credit	(103,820)	45,514	(20,655)
Payment of principal obligations under equipment notes	(32,584)	(4,550)	0
Payment of principal obligations under finance leases	(1,238)	(1,201)	(1,081)
Borrowings under equipment notes	0	35,068	31,486
Proceeds from exercise of stock options	749	341	1,897
Debt refinancing costs	0	(1,122)	0
Repurchase of common shares	(652)	(778)	(1,043)
Other financing activities	13,249	84	38
Net cash flows provided by (used in) financing activities	(124,296)	73,356	10,642
Effect of exchange rate changes on cash	326	132	(64)
Net increase in cash and cash equivalents	10,271	4,890	2,164
Cash and cash equivalents:
Beginning of period	12,397	7,507	5,343
End of period	22,668	12,397	7,507
Cash paid during the period for:
Income taxes payments	24,185	13,381	7,247
Interest payments	4,071	5,737	3,097
Noncash investing activities:
Acquisition of property and equipment for which payment is pending	$ 349	$ 43	$ 953