CONSOLIDATED STATEMENTS OF CASH FLOWS $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Cash flows from operating activities:
Net income	$ 76,850	$ 27,725	$ 37,151
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	57,614	61,433	58,408
Amortization of intangible assets	8,689	6,597	6,793
Goodwill and intangible asset impairment	477	2,716	401
Stock-based compensation expense	1,126	1,627	1,050
Gain on short-term investments	(5,817)
Gain on sale of property and equipment	(4,434)	(4,677)	(2,116)
Net deferred tax liabilities (assets)	3,741	10,905	(7,004)
Other non-cash items	203	174	165
Changes in assets and liabilities:
Customer retention deposits	(519)	2,117	(2,117)
Accounts receivable	40,546	(65,806)	19,528
Costs and estimated earnings in excess of billings	(20,894)	(22,163)	(47,499)
Other current assets	16,976	17,491	4,784
Other long-term assets	28	(1,792)	189
Accounts payable	(30,547)	42,934	(5,086)
Billings in excess of costs and estimated earnings	45,981	(27,519)	(19,619)
Contingent earnout liabilities	(484)		(6,722)
Accrued expenses and other current liabilities	(972)	14,492	11,729
Other long-term liabilities	378	(3,677)	(1,658)
Net cash provided by operating activities	188,942	62,577	48,377
Cash flows from investing activities:
Purchase of property and equipment	(79,782)	(58,027)	(67,097)
Proceeds from sale of property and equipment	8,736	9,603	9,889
Purchase of short-term investments	(13,588)
Sale of short-term investments	19,405		30,992
Cash paid for acquisitions	(66,205)	(10,997)	(22,302)
Net cash used in investing activities	(131,434)	(59,421)	(48,518)
Cash flows from financing activities:
Proceeds from issuance of long-term debt	55,000	45,000	75,278
Repayment of capital leases	(322)	(793)	(1,336)
Repayment of long-term debt	(61,816)	(57,719)	(43,927)
Payment of debt issuance costs for amended and restated credit agreement	(631)
Proceeds from issuance of common stock purchased under a long-term incentive plan	1,148	1,440	1,621
Cash distribution to non-controlling interest holder			(29)
Repurchase of common stock	(4,999)	(4,999)
Dividends paid	(11,326)	(11,384)	(9,809)
Net cash (used in) provided by financing activities	(22,946)	(28,455)	21,798
Net change in cash and cash equivalents	34,562	(25,299)	21,657
Cash and cash equivalents at beginning of the period	135,823	161,122	139,465
Cash and cash equivalents at end of the period	170,385	135,823	161,122
Cash paid:
Interest	7,965	8,819	7,688
Income taxes, net of refunds received	25,984	8,624	18,696
SUPPLEMENTAL DISCLOSURES OF NONCASH INVESTING AND FINANCING ACTIVITIES
Obligations incurred for the acquisition of property	4,163		25
Dividends declared and not yet paid	$ 3,087	$ 2,839	$ 2,842