CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Cash flows from operating activities:
Net income	$ 44,170	$ 39,284	$ 106,676	$ 140,726
Adjustments to reconcile net income to cash provided by operating activities:
Depreciation and amortization			97,864	60,746
Share-based compensation expense			80,360	54,112
Operating lease right-of-use assets expense			7,016	4,233
Deferred income tax benefit			(15,681)	(2,458)
Changes in operating assets and liabilities, exclusive of effects of    acquired companies:
Accounts receivable			2,403	9,394
Income tax receivable			24,171	(14,270)
Prepaid expenses and other current assets			(10,456)	(7,333)
Accounts payable			(64,383)	(3,904)
Operating lease liabilities			(3,904)	(5,121)
Accrued liabilities			4,817	6,276
Deferred revenue			29,609	23,927
Increase in other long-term liabilities			(1,749)	0
Net cash provided by operating activities			256,743	266,328
Cash flows from investing activities:
Additions to property and equipment			(20,770)	(19,064)
Purchase of marketable security investments			(75,684)	(111,329)
Proceeds from marketable security investments			114,563	61,794
Purchase of investment in common shares			0	(10,000)
Proceeds from the sale of investment in preferred shares			0	15,000
Investment in software			(14,966)	(4,316)
Cost of acquisitions, net of cash acquired			(2,088,394)	(261)
Other			463	13
Net cash used by investing activities			(2,084,788)	(68,163)
Cash flows from financing activities:
Net borrowings on revolving credit facility			0	0
Payment on term loans			(57,500)	0
Proceeds from term loans			900,000	0
Proceeds from issuance of convertible senior notes			600,000	0
Payment of debt issuance costs			(27,165)	0
Purchase of treasury shares			(12,975)	(15,484)
Payment of contingent consideration			0	(5,619)
Proceeds from exercise of stock options			46,433	100,732
Contributions from employee stock purchase plan			9,757	8,209
Net cash provided by financing activities			1,458,550	87,838
Net (decrease) increase in cash and cash equivalents			(369,495)	286,003
Cash and cash equivalents at beginning of period			603,623	232,682	$ 232,682
Cash and cash equivalents at end of period	$ 234,128	$ 518,685	$ 234,128	$ 518,685	$ 603,623