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	$ 112,903	$ 55,272	$ 64,896
Adjustments to reconcile net income to net cash provided by operating activities—
Amortization of identifiable intangible assets	20,089	17,404	8,185
Depreciation expense	22,600	20,052	17,981
Goodwill impairment		1,105
Bad debt expense (benefit)	3,562	182	(27)
Deferred tax provision (benefit)	4,456	4,178	(1,239)
Amortization of debt financing costs	383	376	367
Gain on sale of assets	(945)	(670)	(761)
Changes in the fair value of contingent earn-out obligations	2,066	(3,715)	(731)
Stock-based compensation	7,161	6,377	5,041
(Increase) decrease in—
Receivables, net	(68,621)	(37,799)	7,038
Inventories	(1,538)	(584)	213
Prepaid expenses and other current assets	519	2,467	(8,850)
Costs and estimated earnings in excess of billings and unbilled accounts receivable	(14,444)	1,869	3,144
Other noncurrent assets	(114)	1,005	(143)
Increase (decrease) in—
Accounts payable and accrued liabilities	47,871	22,068	2,736
Billings in excess of costs and estimated earnings	16,786	13,265	(8,351)
Other long-term liabilities	(5,544)	11,238	1,689
Net cash provided by operating activities	147,190	114,090	91,188
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of property and equipment	(27,268)	(35,467)	(23,217)
Proceeds from sales of property and equipment	1,698	1,359	1,062
Cash paid for acquisitions, net of cash acquired	(70,140)	(94,860)	(57,163)
Net cash used in investing activities	(95,710)	(128,968)	(79,318)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from revolving line of credit	124,000	177,000	144,000
Payments on revolving line of credit	(119,000)	(132,000)	(154,000)
Payments on other debt	(1,127)	(835)	(592)
Payments on capital lease obligations		(256)	(251)
Debt financing costs	(844)		(789)
Payments of dividends to stockholders	(12,268)	(10,987)	(10,264)
Share repurchase	(28,533)	(9,007)	(13,088)
Shares received in lieu of tax withholding	(1,540)	(1,419)	(1,304)
Proceeds from exercise of options	3,105	2,052	1,578
Deferred acquisition payments	(750)	(2,802)	(1,350)
Payments for contingent consideration arrangements	(5,445)	(2,400)	(200)
Net cash provided by (used in) financing activities	(42,402)	19,346	(36,260)
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	9,078	4,468	(24,390)
CASH AND CASH EQUIVALENTS, beginning of year	36,542	32,074	56,464
CASH AND CASH EQUIVALENTS, end of year	$ 45,620	$ 36,542	$ 32,074