CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Cash Flows from Operating Activities:
Net income	$ 102,709	$ 89,476
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	21,355	20,804
Benefit of deferred income taxes	3,294	3,005
Share-based compensation expense	6,334	5,960
Other	628	1,091
Changes in assets and liabilities:
Accounts receivable	(33,421)	(21,800)
Inventories	(14,521)	(8,070)
Other assets and liabilities	(49,601)	(52,302)
Accounts payable	699	(1,939)
Deferred revenue	(3,098)	(1,327)
Net cash provided by operating activities	34,378	34,898
Cash Flows from Investing Activities:
Purchases of property and equipment	(38,206)	(23,726)
Purchase of marketable securities	0	(87)
Proceeds from the sale and maturities of marketable securities	0	284,125
Net cash (used) provided by investing activities	(38,206)	260,312
Cash Flows from Financing Activities:
Repayments on revolving credit facilities, net	(52,024)	(247,500)
Issuance of senior notes	100,000	0
Debt issuance costs	(30)	0
Payment of acquisition-related contingent consideration	(573)	0
Repurchases of common stock	(54,302)	(83,487)
Proceeds from exercises of stock options and employee stock purchase plans	11,551	14,551
Shares withheld for statutory tax withholding on restricted stock	(7,403)	(8,555)
Net cash used by financing activities	(2,781)	(324,991)
Net effect of changes in exchange rates on cash	(569)	1,335
Net decrease in cash and cash equivalents	(7,178)	(28,446)
Cash and cash equivalents at beginning of period	123,794	187,675
Cash and cash equivalents at end of period	$ 116,616	$ 159,229