Consolidated Statement 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 (loss) income	$ (50,128)	$ 5,844	$ 51,788	$ 74,589
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization			35,946	25,836
Bad debt allowance (recovery)			466	(541)
Deferred income taxes			(17,788)	7,853
Stock-based compensation expense			32,853	23,617
Amortization and write-off of deferred debt issuance costs			4,160	430
Change in fair value of derivative			(9,198)	3,365
Change in fair value of contingent consideration			0	(1,340)
Foreign currency remeasurement loss (gain)			103	(9,067)
Loss from investment accounted for using the equity method, net of tax	664	581	2,939	1,447
Changes in assets and liabilities, net of effect from acquisitions:
Accounts receivable			26,305	46,661
Prepaid and other assets			11,310	8,907
Accounts payable, accruals, and other liabilities			31,766	31,486
Deferred compensation plan liabilities			86,608	2,487
Deferred revenues			(36,598)	(35,134)
Income taxes payable, net of prepaid income taxes			(13,243)	(4,571)
Net cash provided by operating activities			207,417	176,025
Cash flows from investing activities:
Purchases of property and equipment and investment in capitalized software			(11,152)	(13,533)
Acquisitions, net of cash acquired of $37,837 and $2,064, respectively			(1,033,695)	(68,920)
Other investing activities			(3,000)	(6,355)
Net cash used in investing activities			(1,047,847)	(88,808)
Cash flows from financing activities:
Proceeds from credit facilities			682,083	432,375
Payments of credit facilities			(860,228)	(201,125)
Proceeds from convertible senior notes, net of discounts and commissions			1,233,377	0
Payments of debt issuance costs			(5,643)	(432)
Purchase of capped call options			(51,555)	0
Proceeds from term loan			0	125,000
Payments of financing leases			(147)	(141)
Payments of acquisition debt and other consideration			(741)	(2,034)
Payments of dividends			(25,076)	(412,852)
Payments for shares acquired including shares withheld for taxes			(111,306)	(72,476)
Proceeds from Common Stock Purchase Agreement			0	58,349
Proceeds from stock purchases under employee stock purchase plan			3,846	0
Proceeds from exercise of stock options			5,039	3,206
Net cash provided by (used in) financing activities			869,649	(70,130)
Effect of exchange rate changes on cash and cash equivalents			4,530	(590)
Increase in cash and cash equivalents			33,749	16,497
Cash and cash equivalents, beginning of year			122,006	121,101	$ 121,101
Cash and cash equivalents, end of period	$ 155,755	$ 137,598	155,755	137,598	$ 122,006
Supplemental information:
Cash paid for income taxes			32,359	17,338
Income tax refunds			7,820	1,630
Interest paid			3,281	4,658
Non-cash investing and financing activities:
Shares issued related to acquisition			182,390	0
Contingent acquisition consideration			5,581	1,902
Deferred, non-contingent consideration, net			10,081	(141)
Convertible senior notes expenses included in Accounts payable			375	0
Capped call options expenses included in Accounts payable			50	0
Share-settled Executive Bonus Plan awards			16,015	0
Deferred compensation plan elective participant deferrals			$ 2,020	$ 2,602