Consolidated Statement Of Cash Flows - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash flows from operating activities:
Net income	$ 128,687,000	$ 139,425,000	$ 152,439,000
Adjustments to reconcile net earnings to net cash provided by operating activities:
Depreciation and amortization	187,174,000	162,041,000	122,091,000
Amortization of financing costs and discounts	11,385,000	11,952,000	9,818,000
Share-based compensation	28,093,000	22,737,000	13,650,000
Provision for doubtful accounts	17,338,000	13,159,000	13,169,000
Deferred income taxes, net	25,050,000	(21,432,000)	(13,779,000)
Loss on extinguishment of debt and related interest expense	0	7,962,000	0
Gain on sale of businesses	0	(27,681,000)	0
Changes in fair value of contingent consideration	18,944,000	2,300,000	4,850,000
Gain on available-for-sale investment	0	0	(7,716,000)
Loss on equity investments	10,506,000	0	0
Decrease (increase) in:
Accounts receivable	4,034,000	(37,546,000)	(30,687,000)
Prepaid expenses and other current assets	2,211,000	4,001,000	(957,000)
Other assets	2,391,000	(2,712,000)	(497,000)
Increase (decrease) in:
Accounts payable and accrued expenses	(35,220,000)	(34,116,000)	6,363,000
Income taxes payable	(29,042,000)	14,888,000	25,409,000
Deferred revenue	11,991,000	941,000	(4,213,000)
Liability for uncertain tax positions	7,694,000	4,936,000	10,620,000
Other long-term liabilities	10,089,000	3,564,000	(18,173,000)
Net cash provided by operating activities	401,325,000	264,419,000	282,387,000
Tax Cuts And Jobs Act Of 2017, Incomplete Accounting, Transition Tax For Accumulated Foreign Earnings, Provisional Income Tax Expense	0.000	0.246	0.00
Cash flows from investing activities:
Purchases of equity method investment	(36,635,000)	0	0
Maturity of investments	0	0	241,817,000
Purchases of available-for-sale investments	(500,000)	(4,000)	(80,918,000)
Purchases of property and equipment	(56,379,000)	(39,595,000)	(24,746,000)
Acquisition of businesses, net of cash received	(312,430,000)	(174,951,000)	(580,691,000)
Proceeds from sale of businesses, net of cash divested	0	58,300,000	0
Purchases of intangible assets	(669,000)	(2,240,000)	(4,321,000)
Net cash used in investing activities	(406,613,000)	(158,490,000)	(448,859,000)
Cash flows from financing activities:
Issuance of long-term debt, net	0	636,485,000	0
Payment of debt	(2,204,000)	(255,000,000)	0
Proceeds from line of credit, net	0	44,981,000	178,710,000
Repayment of line of credit	0	(225,000,000)	0
Repurchase of common stock	(47,102,000)	(9,850,000)	(56,496,000)
Issuance of common stock under employee stock purchase plan	2,084,000	259,000	254,000
Exercise of stock options	1,540,000	1,108,000	3,570,000
Dividends paid	(81,679,000)	(73,469,000)	(65,835,000)
Deferred payments for acquisitions	(3,558,000)	(7,637,000)	(20,832,000)
Other	(443,000)	(54,000)	1,779,000
Net cash (used in) provided by financing activities	(131,362,000)	111,823,000	41,150,000
Effect of exchange rate changes on cash and cash equivalents	(4,821,000)	9,243,000	(6,258,000)
Net change in cash and cash equivalents	(141,471,000)	226,995,000	(131,580,000)
Cash and cash equivalents at beginning of year	350,945,000	123,950,000	255,530,000
Cash and cash equivalents at end of year	$ 209,474,000	$ 350,945,000	$ 123,950,000