Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Cash flows from operating activities:
Net income	$ 35,290	$ 62,991
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	42,660	24,428
Non-cash interest expense and other	2,817	1,134
Change in fair value of contingent consideration	5,000	(2,158)
Increase in allowance for credit losses and sales credits	6,742	4,978
Provision for deferred income taxes	(9,827)	(10,328)
Share-based compensation	11,274	8,888
Loss on disposal or sale of fixed assets	3,321	39
Amortization of discount on investments	(71)	(229)
Net loss on deferred compensation balances	379	0
Non-cash lease expense	180	(106)
Changes in assets and liabilities, net of effects from acquisitions:
Accounts receivable	2,160	12,427
Accounts receivable, subcontractor	14,245	84
Income taxes receivable	6,157	(1,673)
Prepaid expenses	(3,260)	(1,523)
Other current assets	584	583
Other assets	3,144	(8,763)
Accounts payable and accrued expenses	(14,035)	(29,471)
Accrued compensation and benefits	(1,187)	11,774
Other liabilities	22,764	(5,852)
Deferred revenue	(72)	(2,025)
Restricted investments balance	6	93
Net cash provided by operating activities	128,271	65,291
Cash flows from investing activities:
Purchase and development of fixed assets	(19,727)	(15,532)
Purchase of investments	(23,129)	(13,281)
Proceeds from maturity of investments	14,100	22,670
Payments to fund deferred compensation plan	(6,191)	(5,279)
Purchase of convertible promissory note	(490)	0
Cash paid for acquisitions, net of cash and restricted cash received	(476,491)	(228,149)
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	(513,262)	(240,691)
Cash flows from financing activities:
Payments on term loans	(1,563)	0
Proceeds from term loans	250,000	150,000
Payments on revolving credit facility	(125,000)	(25,000)
Proceeds from revolving credit facility	225,000	101,000
Repurchase of common stock	0	(18,705)
Payment of financing costs	(4,181)	(777)
Earn-out payments for prior acquisitions	(10,622)	(5,700)
Cash paid for shares withheld for taxes	(4,640)	(11,533)
Net cash provided by financing activities	328,994	189,285
Effect of exchange rate changes on cash	(105)	(190)
Net increase (decrease) in cash, cash equivalents and restricted cash	(56,102)	13,695
Cash, cash equivalents and restricted cash at the beginning of period	153,962	84,324
Cash, cash equivalents and restricted cash at the end of period	97,860	98,019
Supplemental disclosures of cash flow information:
Cash paid for amounts included in the measurement of operating lease liabilities	10,112	8,694
Cash paid for interest (net of $208 and $230 capitalized for the six months ended June 30, 2020 and 2019, respectively)	12,759	11,714
Cash paid for income taxes	59	27,369
Acquisitions:
Fair value of tangible assets acquired in acquisitions, net of cash and restricted cash received	35,868	27,674
Goodwill	274,560	149,941
Intangible assets	228,000	96,180
Liabilities assumed	(61,937)	(33,524)
Earn-out liabilities	0	(12,122)
Net cash paid for acquisitions	476,491	228,149
Supplemental disclosures of non-cash investing and financing activities:
Purchase of fixed assets recorded in accounts payable and accrued expenses	$ 1,225	$ 2,352