CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Cash flows from operating activities:
Net income	$ 53,212	$ 53,042
Adjustments to reconcile net income to net cash (used in) provided by operating activities (net of effect of acquisitions):
Depreciation	47,708	43,064
Amortization of intangible assets	8,287	6,184
Intangible asset impairment		477
Stock-based compensation expense	748	911
Gain on short-term investments		(5,980)
Gain on sale of property and equipment	(3,212)	(3,880)
Other non-cash items	180	131
Changes in assets and liabilities:
Accounts receivable	(78,819)	54,865
Contract assets	(85,817)	(42,011)
Other current assets	11,061	7,186
Other long-term assets	(957)	(2,745)
Accounts payable	24,099	(17,813)
Contract liabilities	(11,061)	46,210
Accrued liabilities	16,400	17,848
Other long-term liabilities	5,298	3,943
Net cash (used in) provided by operating activities	(12,873)	161,432
Cash flows from investing activities:
Purchase of property and equipment	(80,766)	(57,346)
Issuance of a note receivable	(15,000)
Proceeds from a note receivable	15,000
Proceeds from sale of property and equipment	9,655	7,027
Purchase of short-term investments		(13,588)
Sale of short-term investments		350
Cash paid for acquisitions, net of cash and restricted cash acquired	(111,030)	(66,205)
Net cash used in investing activities	(182,141)	(129,762)
Cash flows from financing activities:
Borrowings under revolving line of credit	170,000
Payments on revolving line of credit	(170,000)
Proceeds from issuance of long-term debt	239,467	30,000
Cash distribution to non-controlling interest holder	(8,750)
Payment of contingent earnout liability	(1,200)
Repayment of long-term debt and capital leases	(127,363)	(41,279)
Payment of debt issuance cost	(1,041)	(631)
Proceeds from issuance of common stock purchased under a long-term incentive plan	1,498	1,148
Repurchase of common stock	(8,479)	(4,999)
Dividends paid	(9,271)	(8,497)
Net cash provided by (used in) financing activities	84,861	(24,258)
Effect of exchange rate changes on cash and cash equivalents	(193)
Net change in cash, cash equivalents and restricted cash	(110,346)	7,412
Cash and cash equivalents at beginning of the period	170,385	135,823
Cash and cash equivalents at end of the period	60,039	143,235
Cash paid:
Interest	11,658	6,236
Income taxes, net of refunds received	5,379	25,618
SUPPLEMENTAL DISCLOSURES OF NONCASH INVESTING AND FINANCING ACTIVITIES
Obligations incurred for the acquisition of property		4,163
Dividends declared and not yet paid	$ 3,072	$ 2,829