Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Cash flows from operating activities:
Net income	$ 61,357	$ 86,506
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	70,077	41,513
Non-cash interest expense and other	3,727	1,816
Write-off of fees on credit facilities	1,773	0
Change in fair value of contingent consideration	(1,700)	2,283
Increase in allowance for credit losses and sales credits	7,580	6,809
Provision for deferred income taxes	(17,923)	(3,700)
Share-based compensation	15,046	11,713
Loss on disposal or sale of fixed assets	3,664	449
Amortization of discount on investments	(96)	(276)
Net loss on deferred compensation balances	798	0
Non-cash lease expense	244	(1)
Changes in assets and liabilities, net of effects from acquisitions:
Accounts receivable	15,151	25,146
Accounts receivable, subcontractor	16,414	(12,610)
Income taxes receivable	6,157	(3,401)
Prepaid expenses	(3,361)	1,118
Other current assets	2,977	1,332
Other assets	3,378	(8,790)
Accounts payable and accrued expenses	(5,484)	(14,277)
Accrued compensation and benefits	7,630	19,787
Other liabilities	29,592	(7,273)
Deferred revenue	(32)	(2,038)
Restricted investments balance	12	99
Net cash provided by operating activities	216,981	146,205
Cash flows from investing activities:
Purchase and development of fixed assets	(27,357)	(24,776)
Purchase of investments	(37,418)	(16,759)
Proceeds from maturity of investments	21,500	28,635
Payments to fund deferred compensation plan	(7,171)	(11,364)
Proceeds from sale of equity investment	303	0
Purchase of convertible promissory notes	(490)	0
Cash paid for acquisitions, net of cash and restricted cash received	(476,491)	(228,222)
Cash paid for other intangibles	(1,400)	(1,120)
Cash received for working capital adjustments for prior year acquisitions	66	0
Net cash used in investing activities	(528,458)	(253,606)
Cash flows from financing activities:
Payments on term loans	(203,125)	(938)
Proceeds from term loans	250,000	150,000
Payments on revolving credit facility	(205,000)	(75,000)
Proceeds from revolving credit facility	245,000	101,000
Proceeds from senior notes	202,000	0
Repurchase of common stock	0	(18,705)
Payment of financing costs	(6,898)	(875)
Earn-out payments for prior acquisitions	(10,622)	(5,700)
Cash paid for shares withheld for taxes	(4,798)	(13,342)
Net cash provided by financing activities	266,557	136,440
Effect of exchange rate changes on cash	(119)	(58)
Net increase (decrease) in cash, cash equivalents and restricted cash	(45,039)	28,981
Cash, cash equivalents and restricted cash at beginning of period	153,962	84,324
Cash, cash equivalents and restricted cash at end of period	108,923	113,305
Supplemental disclosures of cash flow information:
Cash paid for amounts included in the measurement of operating lease liabilities	15,079	13,294
Cash paid for interest (net of $300 and $363 capitalized for the nine months ended September 30, 2020 and 2019, respectively)	13,848	14,988
Cash paid for income taxes	30,727	32,457
Acquisitions:
Fair value of tangible assets acquired in acquisitions, net of cash and restricted cash received	35,704	28,542
Goodwill	274,427	148,095
Intangible assets	228,000	98,580
Liabilities assumed	(61,640)	(34,873)
Earn-out liabilities	0	(12,122)
Net cash paid for acquisitions	476,491	228,222
Supplemental disclosures of non-cash investing and financing activities:
Purchase of fixed assets recorded in accounts payable and accrued expenses	$ 1,007	$ 2,142