Condensed Consolidated Statement of Cash Flows - USD ($)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Cash flows from operating activities:
Net income	$ 60,883,000	$ 30,745,000	$ 92,580,000	$ 95,783,000
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization			163,680,000	170,409,000
Amortization of financing costs and discounts			21,393,000	9,072,000
Non-cash operating lease costs			15,686,000	14,474,000
Share-based compensation			18,643,000	18,394,000
Provision for doubtful accounts			9,508,000	9,217,000
Deferred income taxes, net			7,815,000	2,850,000
Gain on sale of businesses	(17,122,000)	0	(17,122,000)	0
Lease asset impairments and other charges		0	9,786,000	0
Changes in fair value of contingent consideration			(243,000)	8,044,000
Foreign currency remeasurement gain			(15,919,000)	0
Loss (income) on equity method investments			10,799,000	(166,000)
Loss on equity and debt investments			20,826,000	0
Decrease (increase) in:
Accounts receivable			57,560,000	29,953,000
Prepaid expenses and other current assets			(3,279,000)	(10,094,000)
Other assets			543,000	(1,528,000)
Increase (decrease) in:
Accounts payable and accrued expenses			(26,430,000)	623,000
Income taxes payable			(496,000)	(15,179,000)
Deferred revenue			(10,494,000)	777,000
Operating lease liabilities			(12,857,000)	(13,612,000)
Liability for uncertain tax positions			7,746,000	(9,144,000)
Other long-term liabilities			6,284,000	(566,000)
Net cash provided by operating activities			356,009,000	309,307,000
Cash flows from investing activities:
Distribution from equity method investment			0	10,288,000
Purchases of equity method investment			(29,979,000)	(22,338,000)
Purchases of equity investments			(843,000)	0
Purchases of property and equipment			(71,266,000)	(49,483,000)
Acquisition of businesses, net of cash received			(27,156,000)	(411,349,000)
Proceeds from sale of businesses			24,353,000	0
Proceeds from sale of assets			507,000	0
Purchases of intangible assets			(2,902,000)	(46,000)
Net cash used in investing activities			(107,286,000)	(472,928,000)
Cash flows from financing activities:
Payment of note payable			(400,000)	(5,100,000)	$ (5,100,000)
Proceeds from line of credit			0	185,000,000
Repayment of line of credit			0	(57,000,000)
Repurchase of common stock			(238,905,000)	(20,562,000)
Issuance of common stock under employee stock purchase plan			3,303,000	1,995,000
Exercise of stock options			952,000	5,274,000
Dividends paid			0	(43,966,000)
Deferred payments for acquisitions			(20,427,000)	(17,734,000)
Other			(1,377,000)	(1,055,000)
Net cash (used in) provided by financing activities			(256,854,000)	46,852,000
Effect of exchange rate changes on cash and cash equivalents			446,000	(520,000)
Net change in cash and cash equivalents			(7,685,000)	(117,289,000)
Cash and cash equivalents at beginning of period			575,615,000	209,474,000	209,474,000
Cash and cash equivalents at end of period	$ 567,930,000	$ 92,185,000	$ 567,930,000	$ 92,185,000	$ 575,615,000