CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 150,139	$ 114,324	$ 112,903
Adjustments to reconcile net income to net cash provided by operating activities-
Amortization of identifiable intangible assets	32,698	27,082	20,089
Depreciation expense	27,931	24,490	22,600
Change in right-of-use assets	16,692	16,887
Bad debt expense	5,253	2,978	3,562
Deferred tax provision (benefit)	(7,953)	(4,251)	4,456
Amortization of debt financing costs	544	387	383
Gain on sale of assets	(1,445)	(1,701)	(945)
Changes in the fair value of contingent earn-out obligations	(9,119)	2,991	2,066
Stock-based compensation	6,934	5,878	7,161
(Increase) decrease in-
Receivables, net	38,486	(49,508)	(68,621)
Inventories	(1,457)	2,366	(1,538)
Prepaid expenses and other current assets	(4,855)	(15,519)	519
Costs and estimated earnings in excess of billings and unbilled accounts receivable	2,706	(4,312)	(14,444)
Other noncurrent assets	(1,373)	(735)	(114)
Increase (decrease) in-
Accounts payable and accrued liabilities	11,087	31,046	47,871
Billings in excess of costs and estimated earnings	19,434	4,376	16,786
Other long-term liabilities	808	(14,751)	(5,544)
Net cash provided by operating activities	286,510	142,028	147,190
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of property and equipment	(24,131)	(31,750)	(27,268)
Proceeds from sales of property and equipment	2,270	2,159	1,698
Proceeds from sale of business		1,611
Cash paid for acquisitions, net of cash acquired	(185,941)	(196,470)	(70,140)
Net cash used in investing activities	(207,802)	(224,450)	(95,710)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from revolving credit facility	268,000	356,000	124,000
Payments on revolving credit facility	(226,000)	(228,000)	(119,000)
Payments on term loan	(15,000)
Payments on other debt	(46,534)	(3,784)	(1,127)
Debt financing costs		(1,405)	(844)
Payments of dividends to stockholders	(15,499)	(14,543)	(12,268)
Share repurchase	(30,120)	(19,550)	(28,533)
Shares received in lieu of tax withholding	(1,076)	(1,498)	(1,540)
Proceeds from exercise of options	2,144	2,350	3,105
Deferred acquisition payments	(650)	(637)	(750)
Payments for contingent consideration arrangements	(9,865)	(1,343)	(5,445)
Net cash provided by (used in) financing activities	(74,600)	87,590	(42,402)
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	4,108	5,168	9,078
CASH AND CASH EQUIVALENTS, beginning of period	50,788	45,620	36,542
CASH AND CASH EQUIVALENTS, end of period	$ 54,896	$ 50,788	$ 45,620