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	$ 119,738	$ 57,425	$ 30,880
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation expense	50,373	53,214	47,959
Amortization of intangible assets	15,015	16,003	20,721
Amortization of debt issuance costs	1,684	1,684	3,114
Deferred income taxes	1,266	2,318	(3,571)
Non-cash stock compensation expense	11,315	6,769	7,252
Gain on sale of property, equipment and real estate	(3,321)	(1,683)	(1,396)
Gain on insurance proceeds	0	(1,991)	(1,003)
Impairment of assets	0	435	11,928
Loss on debt extinguishment	0	0	12,529
Amortization of inventory step-up charges	0	0	2,884
Other non-cash adjustments	613	552	98
Change in assets and liabilities, net of effects of acquisitions
Accounts receivable, net of allowances	16,078	(3,252)	(10,128)
Inventories, net	3,257	(32,297)	(31,200)
Contract assets	5,565	0	0
Costs in excess of billings on uncompleted contracts	0	(2,364)	(3,845)
Income taxes payable/receivable	4,650	(1,311)	9,627
Prepaid expenses and other current assets	2,588	(13,191)	(12,208)
Other long-term assets	(69)	3,458	(126)
Accounts payable	(51,348)	3,477	28,592
Accrued expenses and other liabilities	19,066	5,417	(5,859)
Contract liabilities	8,609	0	0
Billings in excess of costs on uncompleted contracts	0	2,737	(197)
Insurance reserves	4,502	(3,239)	(16)
Other long-term liabilities	444	(227)	853
Net cash provided by operating activities	210,025	93,934	106,888
Cash flows from investing activities
Purchases of property, equipment and real estate	(55,174)	(63,278)	(38,067)
Purchases of businesses, net of cash acquired	(20,970)	(38,438)	0
Proceeds from sale of property, equipment and real estate	11,432	13,445	3,187
Proceeds from sale of business	7,773	0	0
Insurance proceeds	1,991	0	1,151
Net cash used in investing activities	(54,948)	(88,271)	(33,729)
Cash flows from financing activities
Proceeds from revolving line of credit	854,946	995,306	1,544,064
Repayments of proceeds from revolving line of credit	(859,408)	(990,844)	(1,696,324)
Payments on capital lease obligations	(7,759)	(9,926)	(8,800)
Principal payments on other notes	(336)	(2,627)	(3,303)
Secured borrowings	431	2,880	1,427
Proceeds from exercise of stock options	1,327	3,396	1,301
Repurchases of common stock under share repurchase program	(2,891)	0	0
Repurchases of common stock related to equity award activity	(2,044)	(977)	(2,023)
Holdback payments	(370)	0	0
Payments of debt issuance costs	0	(38)	(7,011)
Proceeds from issuance of Senior Notes	0	0	350,000
Redemption of Extinguished Senior Notes	0	0	(250,000)
Proceeds from issuance of common stock, net of offering costs	0	0	13,776
Payments of debt extinguishment costs	0	0	(8,438)
Net cash used in financing activities	(16,104)	(2,830)	(65,331)
Net increase in cash and cash equivalents	138,973	2,833	7,828
Cash and cash equivalents
Beginning of period	11,750	8,917	1,089
End of period	150,723	11,750	8,917
Supplemental disclosure of cash flow information
Interest paid	22,361	24,210	28,081
Cash paid for income taxes, net	31,260	22,858	8,210
Non-cash investing and financing transactions
Acquisition-related holdback payments due at a future date	1,403	375	0
Accrued purchases of property and equipment	1,963	811	505
Assets acquired under capital lease obligations	$ 821	$ 2,481	$ 15,089