CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Cash Flows from Operating Activities:
Net income	$ 407,173	$ 337,248
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	71,437	65,422
Impairment charge	1,993	0
Provision for credit losses (Note 2 & Note 6)	5,235	618
Deferred income taxes	(3,363)	2,403
Share-based compensation expense	23,008	22,623
Other	488	879
Changes in assets and liabilities:
Accounts receivable	(72,409)	(24,451)
Inventories	(25,091)	(36,582)
Other assets and liabilities	30,579	(54,770)
Accounts payable	512	1,181
Deferred revenue	(10,433)	(10,826)
Net cash provided by operating activities	429,129	303,745
Cash Flows from Investing Activities:
Purchases of property and equipment	(92,768)	(109,058)
Acquisition of intangible assets	(668)	(255)
Acquisitions of a business and equity investment, net of cash acquired	(250)	(304)
Net cash used by investing activities	(93,686)	(109,617)
Cash Flows from Financing Activities:
Repayments on revolving credit facilities, net	(289,625)	(169,532)
Issuance of senior notes	200,000	100,000
Debt issuance costs	(4,995)	(154)
Payment of acquisition-related contingent consideration	(1,580)	(2,255)
Repurchases of common stock, net	(182,815)	(160,969)
Proceeds from exercises of stock options and employee stock purchase plans	39,230	28,739
Shares withheld for statutory tax withholding on restricted stock	(9,029)	(7,849)
Net cash used by financing activities	(248,814)	(212,020)
Net effect of changes in exchange rates on cash	(1,368)	(1,906)
Net increase (decrease) in cash and cash equivalents	85,261	(19,798)
Cash and cash equivalents at beginning of period	90,326	123,794
Cash and cash equivalents at end of period	175,587	103,996
Supplemental Cash Flow Information:
Cash paid for income taxes	79,909	80,036
Unpaid property and equipment, reflected in accounts payable and accrued liabilities	$ 7,708	$ 19,196