CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Cash Flows from Operating Activities:
Net income	$ 337,248	$ 291,370
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	65,422	62,574
Impairment charge	0	2,629
Benefit of deferred income taxes	2,403	12,850
Share-based compensation expense	22,623	18,948
Other	1,497	2,385
Changes in assets and liabilities:
Accounts receivable	(24,451)	(33,041)
Inventories	(36,582)	(27,415)
Other assets and liabilities	(54,770)	(58,214)
Accounts payable	1,181	(1,336)
Deferred revenue	(10,826)	(6,314)
Net cash provided by operating activities	303,745	264,436
Cash Flows from Investing Activities:
Purchases of property and equipment	(109,058)	(82,642)
Purchase of marketable securities	0	(87)
Proceeds from the sale and maturities of marketable securities	0	284,125
Acquisitions of intangible assets	(255)	(450)
Acquisition of a business	(304)	(22,500)
Net cash (used) provided by investing activities	(109,617)	178,446
Cash Flows from Financing Activities:
Repayments on revolving credit facilities, net	(169,532)	(240,500)
Issuance of senior notes	100,000	0
Debt issuance costs	(154)	0
Payment of acquisition-related contingent consideration	(2,255)	(1,266)
Repurchases of common stock, net	(160,969)	(263,712)
Proceeds from exercises of stock options and employee stock purchase plans	28,739	34,595
Shares withheld for statutory tax withholding on restricted stock	(7,849)	(9,110)
Net cash used by financing activities	(212,020)	(479,993)
Net effect of changes in exchange rates on cash	(1,906)	(3,687)
Net decrease in cash and cash equivalents	(19,798)	(40,798)
Cash and cash equivalents at beginning of period	123,794	187,675
Cash and cash equivalents at end of period	103,996	146,877
Supplemental Cash Flow Information:
Unpaid property and equipment, reflected in accounts payable and accrued liabilities	$ 19,196	$ 10,239