CONSOLIDATED STATEMENTS OF CASH FLOWS $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Cash flows from operating activities:
Net income	$ 84,097	$ 87,593	$ 76,850
Adjustments to reconcile net income to net cash provided by operating activities (net of effect of acquisitions):
Depreciation	74,031	67,948	57,614
Amortization of intangible assets	11,369	11,302	8,689
Intangible asset impairment			477
Stock-based compensation expense	1,579	1,253	1,126
Gain on short-term investments			(5,817)
Gain on sale of property and equipment	(11,947)	(3,556)	(4,434)
Other non-cash items	320	275	203
Changes in assets and liabilities:
Accounts receivable	(28,240)	20,912	60,739
Contract assets	19,677	(67,593)	(32,137)
Other current assets	(7,248)	(2,278)	7,507
Net deferred tax liabilities (assets)	13,947	17,155	3,741
Other long-term assets	1,249	244	28
Accounts payable	(13,894)	32,323	(30,547)
Contract liabilities	(1,221)	(43,801)	42,610
Operating lease assets and liabilities, net	(3,191)
Accrued liabilities	(22,924)	5,933	1,915
Other long-term liabilities	377	(895)	378
Net cash provided by operating activities	117,981	126,815	188,942
Cash flows from investing activities:
Purchase of property and equipment	(94,494)	(110,189)	(79,782)
Issuance of a note receivable		(15,000)
Proceeds from a note receivable		15,000
Proceeds from sale of property and equipment	28,621	11,657	8,736
Purchase of short-term investments			(13,588)
Sale of short-term investments			19,405
Cash paid for acquisitions, net of cash and restricted cash acquired		(110,620)	(66,205)
Net cash used in investing activities	(65,873)	(209,152)	(131,434)
Cash flows from financing activities:
Borrowings under revolving line of credit	212,880	190,000
Payments on revolving line of credit	(212,880)	(190,000)
Proceeds from issuance of long-term debt	55,008	255,967	55,000
Repayment of long-term debt	(72,077)	(145,726)	(61,816)
Proceeds from issuance of common stock purchased under a long-term incentive plan	1,804	1,498	1,148
Payment of taxes on conversion of Restricted Stock Units	(1,519)
Payment of contingent earnout liability		(1,200)
Cash distribution to noncontrolling interest holders	(3,505)	(13,084)
Repurchase of common stock from a related party	(50,000)
Repurchase of common stock		(20,000)	(4,999)
Dividends paid	(12,211)	(12,343)	(11,326)
Other	(784)	(1,173)	(953)
Net cash (used in) provided by financing activities	(83,284)	63,939	(22,946)
Effect of exchange rate changes on cash and cash equivalents	399	(924)
Net change in cash and cash equivalents	(30,777)	(19,322)	34,562
Cash and cash equivalents at beginning of the year	151,063	170,385	135,823
Cash and cash equivalents at end of the year	120,286	151,063	170,385
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION
Cash paid for interest	16,155	16,105	7,965
Cash paid for income taxes, net	16,647	14,246	25,984
Leased assets obtained in exchange for new operating leases	154,807
SUPPLEMENTAL DISCLOSURES OF NONCASH INVESTING AND FINANCING ACTIVITIES
Dividends declared and not yet paid	$ 2,919	$ 3,043	$ 3,087