CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Cash flows from operating activities:
Net income	$ 36,544us-gaap_NetIncomeLoss	$ 34,759us-gaap_NetIncomeLoss	$ 34,262us-gaap_NetIncomeLoss
Adjustments to reconcile net income to net cash flows provided by operating activities -
Depreciation and amortization of property and equipment	33,089us-gaap_Depreciation	28,860us-gaap_Depreciation	24,821us-gaap_Depreciation
Amortization of intangible assets	334us-gaap_AmortizationOfIntangibleAssets	335us-gaap_AmortizationOfIntangibleAssets	335us-gaap_AmortizationOfIntangibleAssets
Stock-based compensation expense	4,671us-gaap_ShareBasedCompensation	3,519us-gaap_ShareBasedCompensation	2,923us-gaap_ShareBasedCompensation
Deferred income taxes	3,655us-gaap_DeferredIncomeTaxExpenseBenefit	381us-gaap_DeferredIncomeTaxExpenseBenefit	2,687us-gaap_DeferredIncomeTaxExpenseBenefit
Gain on sale of property and equipment	(142)	(893)	(1,019)
Other non-cash items	139us-gaap_OtherNoncashExpense	151us-gaap_OtherNoncashExpense	110us-gaap_OtherNoncashExpense
Changes in operating assets and liabilities
Accounts receivable, net	15,706	(6,227)	(40,330)
Costs and estimated earnings in excess of billings on uncompleted contracts	(4,090)	21,254	(18,079)
Construction materials inventory	0us-gaap_IncreaseDecreaseInInventories	0us-gaap_IncreaseDecreaseInInventories	4,003us-gaap_IncreaseDecreaseInInventories
Receivable for insurance claims in excess of deductibles	(922)	(10)	(1,257)
Other assets	(1,255)	(2,138)	(1,619)
Accounts payable	(17,303)	(5,289)	11,067
Billings in excess of costs and estimated earnings on uncompleted contracts	(14,831)	20,363	7,644
Accrued self insurance	369	(472)	733
Other liabilities	(988)	469	3,718
Net cash flows provided by operating activities	54,976	95,062	29,999
Cash flows from investing activities:
Proceeds from sale of property and equipment	320	1,151	1,204
Purchases of property and equipment	(39,045)	(42,725)	(37,249)
Net cash flows used in investing activities	(38,725)	(41,574)	(36,045)
Cash flows from financing activities:
Net borrowings (repayments) on revolving credit facility	0	0	(10,000)
Proceeds from exercise of stock options	725	2,304	1,417
Excess tax benefit from stock-based awards	615	1,323	524
Debt issuance costs	0us-gaap_PaymentsOfDebtIssuanceCosts	0us-gaap_PaymentsOfDebtIssuanceCosts	(13)us-gaap_PaymentsOfDebtIssuanceCosts
Repurchase of common shares	(16,447)	(542)	(108)
Other financing activities	38	56	38
Net cash flows provided by (used in) financing activities	(15,069)	3,141	(8,142)
Net increase (decrease) in cash and cash equivalents	1,182	56,629	(14,188)
Cash and cash equivalents:
Beginning of period	76,454	19,825	34,013
End of period	$ 77,636	$ 76,454	$ 19,825

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The aggregate expense charged against earnings to allocate the cost of intangible assets (nonphysical assets not used in production) in a systematic and rational manner to the periods expected to benefit from such assets. As a noncash expense, this element is added back to net income when calculating cash provided by or used in operations using the indirect method.