Condensed Consolidated Statements of Cash Flows (Unaudited) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Cash flows from operating activities:
Net income	$ 5,963	$ 9,018
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	3,621	3,182
Premium amortization and (gains) losses on investments	(105)	71
Stock-based compensation	9,219	7,598
Changes in operating assets and liabilities:
Accounts receivable	286	1,673
Inventories	(12,467)	(81)
Prepaid expenses and other assets	362	(2,036)
Accounts payable	6,902	1,058
Accrued liabilities	3,339	(8,473)
Tax liabilities	187	38
Accrued compensation and related benefits	(1,626)	(63)
Net cash provided by operating activities	15,681	11,985
Cash flows from investing activities:
Property and equipment purchases	(4,703)	(4,516)
Purchases of short-term investments	(59,617)	(41,977)
Proceeds from sale of short-term investments	34,389	27,252
Premiums paid on deferred compensation plan	(2,176)
Net cash used in investing activities	(32,107)	(19,241)
Cash flows from financing activities:
Proceeds from exercise of stock options	1,292	5,554
Proceeds from shares issued under the employee stock purchase plan	1,121	1,053
Repurchases of common shares	(10,405)	(11,358)
Dividends and dividend equivalents paid	(5,859)
Net cash used in financing activities	(13,851)	(4,751)
Effect of change in exchange rates	(23)	(321)
Net decrease in cash and cash equivalents	(30,300)	(12,328)
Cash and cash equivalents, beginning of period	126,266	101,213
Cash and cash equivalents, end of period	95,966	88,885
Supplemental disclosures for cash flow information:
Cash paid for taxes	242	217
Supplemental disclosures of non-cash investing and financing activities:
Liability accrued for property and equipment purchases	1,522	445
Liability accrued for dividends and dividend equivalents	$ 8,459