Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014
Cash flows from operating activities:
Net income	$ 25,063	$ 26,635
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	10,478	9,688
Premium amortization and losses on investments	910	197
Stock-based compensation	29,191	24,872
Excess tax benefit from equity awards	(4,221)
Changes in operating assets and liabilities, net of effects of an acquisition:
Accounts receivable	(4,845)	(516)
Inventories	(26,378)	(1,800)
Prepaid expenses and other assets	141	(1,868)
Accounts payable	3,545	3,864
Accrued liabilities	4,154	(2,885)
Income tax liabilities	1,912	(801)
Accrued compensation and related benefits	5,449	(3,789)
Net cash provided by operating activities	45,399	53,597
Cash flows from investing activities:
Property and equipment purchases	(8,410)	(7,730)
Purchases of short-term investments	(172,651)	(100,706)
Proceeds from sale of short-term investments	131,025	98,752
Premiums paid on deferred compensation plan, net	(3,455)	(4,860)
Cash paid for an acquisition, net of cash acquired		(11,590)
Net cash used in investing activities	(53,491)	(26,134)
Cash flows from financing activities:
Property and equipment purchased on extended payment terms	(150)	(250)
Proceeds from exercise of stock options	6,876	10,403
Proceeds from shares issued under the employee stock purchase plan	2,227	2,078
Repurchases of common shares	(31,735)	(32,976)
Dividends and dividend equivalents paid	(21,853)	(5,817)
Excess tax benefit from equity awards	4,221
Net cash used in financing activities	(40,414)	(26,562)
Effect of change in exchange rates	(1,144)	(302)
Net increase (decrease) in cash and cash equivalents	(49,650)	599
Cash and cash equivalents, beginning of period	126,266	101,213
Cash and cash equivalents, end of period	76,616	101,812
Supplemental disclosures for cash flow information:
Cash paid for taxes and interest	3,070	981
Supplemental disclosures of non-cash investing and financing activities:
Liability accrued for property and equipment purchases	1,003	783
Liability accrued for dividends and dividend equivalents	$ 9,648	6,359
Fair value of contingent consideration related to an acquisition		$ 2,507