Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014
Cash flows from operating activities:
Net income	$ 13,862	$ 15,415
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	7,092	6,300
Premium amortization and (gains) losses on investments	256	134
Stock-based compensation	18,716	16,013
Excess tax benefit from equity awards	(2,648)
Changes in operating assets and liabilities:
Accounts receivable	(1,134)	2,310
Inventories	(24,029)	(1,457)
Prepaid expenses and other assets	405	(1,447)
Accounts payable	4,687	2,968
Accrued liabilities	2,807	(4,955)
Income tax liabilities	1,122	134
Accrued compensation and related benefits	2,213	2,173
Net cash provided by operating activities	23,349	37,588
Cash flows from investing activities:
Property and equipment purchases	(6,655)	(5,958)
Purchases of short-term investments	(129,663)	(86,558)
Proceeds from sale of short-term investments	91,962	78,502
Premiums paid on deferred compensation plan, net	(2,775)	(2,396)
Net cash used in investing activities	(47,131)	(16,410)
Cash flows from financing activities:
Property and equipment purchased on extended payment terms	(150)	(250)
Proceeds from exercise of stock options	6,680	8,623
Proceeds from shares issued under the employee stock purchase plan	1,121	1,053
Repurchases of common shares	(18,129)	(23,796)
Dividends and dividend equivalents paid	(13,842)
Excess tax benefit from equity awards	2,648
Net cash used in financing activities	(21,672)	(14,370)
Effect of change in exchange rates	56	(158)
Net increase (decrease) in cash and cash equivalents	(45,398)	6,650
Cash and cash equivalents, beginning of period	126,266	101,213
Cash and cash equivalents, end of period	80,868	107,863
Supplemental disclosures for cash flow information:
Cash paid for taxes	1,755	633
Supplemental disclosures of non-cash investing and financing activities:
Liability accrued for property and equipment purchases	681	611
Liability accrued for dividends and dividend equivalents	$ 9,121	$ 6,083