CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Cash Flows from Operating Activities:
Net income	$ 582,073	$ 407,173
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	76,901	71,437
Impairment charge	5,148	1,993
Provision for credit losses	1,719	5,235
Deferred income taxes	4,049	(3,363)
Share-based compensation expense	28,042	23,008
Other	2,402	488
Changes in assets and liabilities:
Accounts receivable	(49,050)	(72,409)
Inventories	(46,891)	(25,091)
Other assets and liabilities	(51,961)	30,579
Accounts payable	637	512
Deferred revenue	(7,487)	(10,433)
Net cash provided by operating activities	545,582	429,129
Cash Flows from Investing Activities:
Purchases of property and equipment	(87,761)	(92,768)
Acquisition of intangible assets and equity investments	0	(918)
Acquisitions of a business, net of cash acquired	(161,166)	0
Net cash used by investing activities	(248,927)	(93,686)
Cash Flows from Financing Activities:
Repayments on revolving credit facilities, net	0	(289,625)
Issuance of senior debt	0	200,000
Payment of senior debt	(50,000)	0
Debt issuance costs	0	(4,995)
Payments of acquisition-related contingent considerations and holdbacks	(1,500)	(1,580)
Repurchases of common stock, net	(502,021)	(182,815)
Proceeds from exercises of stock options and employee stock purchase plans	37,428	39,230
Shares withheld for statutory tax withholding payments on restricted stock	(15,501)	(9,029)
Net cash used by financing activities	(531,594)	(248,814)
Net effect of changes in exchange rates on cash	(3,786)	(1,368)
Net (decrease) increase in cash and cash equivalents	(238,725)	85,261
Cash and cash equivalents at beginning of period	383,928	90,326
Cash and cash equivalents at end of period	145,203	175,587
Supplemental Cash Flow Information:
Cash paid for income taxes	96,103	79,909
Unpaid property and equipment, reflected in accounts payable and accrued liabilities	$ 14,734	$ 7,708