Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ (6,654)	$ 41,254	$ 24,437	$ 132,623
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization			83,173	80,427
Impairment losses on long-lived assets	1,700		18,609	0
Impairment losses on equity investment			2,128	0
Stock-based compensation expense			15,138	12,339
Deferred income taxes			8,408	4,085
Other non-cash adjustments — net			(206)	66
Changes in assets and liabilities:
Accounts receivable			(1,385)	14,789
Prepaid expenses and other current assets			(28,599)	(810)
Accounts payable and accrued expenses			11,921	23,824
Income taxes			(18,830)	(11,662)
Deferred revenue			(14,956)	4,046
Leases			30,434	9,565
Other assets			4,192	(344)
Other current and long-term liabilities			35,389	3,482
Net cash provided by operating activities			169,853	272,430
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of fixed assets			(54,494)	(74,492)
Proceeds from the disposal of fixed assets			9,997	4,331
Proceeds from the maturity of debt securities and sale of other investments			10,247	0
Purchases of debt securities and other investments			(6,106)	(20,090)
Purchase of equity method investment			0	(5,772)
Payments and settlements for acquisitions — net of cash acquired			(8,101)	(30,841)
Net cash used in investing activities			(48,457)	(126,864)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from stock issuance — net of issuance costs			249,808	0
Borrowings under revolving credit facility			43,200	172,874
Payments under revolving credit facility			(43,200)	(290,732)
Principal payments of long-term debt			(8,063)	(8,063)
Payments for debt issuance costs			(2,818)	0
Purchase of treasury stock			(32,658)	(12,023)
Taxes paid related to the net share settlement of stock options and restricted stock			(8,896)	(6,531)
Proceeds from issuance of common stock upon exercise of options and restricted stock upon purchase			27,087	21,506
Payments of deferred and contingent consideration for acquisitions			(1,088)	(4,200)
Net cash provided by (used in) financing activities			223,372	(127,169)
Effect of exchange rates on cash, cash equivalents and restricted cash			286	34
Net increase in cash, cash equivalents and restricted cash			345,054	18,431
Cash, cash equivalents and restricted cash — beginning of period			31,192	38,478	$ 38,478
Cash, cash equivalents and restricted cash — end of period	376,246	56,909	376,246	56,909	31,192
RECONCILIATION OF CASH, CASH EQUIVALENTS AND RESTRICTED CASH TO THE CONSOLIDATED BALANCE SHEETS:
Cash and cash equivalents						$ 365,300	$ 27,872	$ 48,529
Restricted cash and cash equivalents, included in prepaid expenses and other current assets						10,946		8,380
Total cash, cash equivalents and restricted cash — end of period	$ 376,246	$ 56,909	376,246	56,909	$ 38,478	376,246	$ 31,192	56,909
SUPPLEMENTAL CASH FLOW INFORMATION:
Cash payments of interest			26,741	33,053
Cash payments of income taxes			8,329	40,691
Cash paid for amounts included in the measurement of lease liabilities			83,874	94,775
NON-CASH TRANSACTIONS:
Fixed asset purchases recorded in accounts payable and accrued expenses			3,377	5,519
Contingent consideration issued for acquisitions						$ 0		$ 16,621
Operating right-of-use assets obtained in exchange for operating lease liabilities — net			$ 88,850	$ 83,772