Consolidated Statements of Cash Flows (Unaudited) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Operating activities
Net income	$ 10,102	$ 8,287
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	2,106	1,734
Stock-based compensation expense	998	865
Deferred taxes	107	148
Excess tax benefit from stock-based compensation	(897)	(4,067)
Amortization of held-to-maturity securities	482	304
Changes in operating assets and liabilities:
Accounts receivable	(3,554)	(1,929)
Inventories	(166)	(183)
Prepaid expenses and other	(828)	393
Income taxes	3,951	2,719
Accounts payable	3,929	1,115
Accrued liabilities and other	(964)	1,759
Net cash provided by operating activities	15,266	11,145
Investing activities
Purchases of property and equipment	(9,892)	(2,548)
Purchases of marketable securities	(32,385)	(41,088)
Proceeds from maturities of marketable securities	26,590	18,313
Net cash used in investing activities	(15,687)	(25,323)
Financing activities
Payments on debt	(50)	(92)
Proceeds from exercises of stock options and other	665	1,619
Excess tax benefit from stock-based compensation	897	4,067
Net cash provided by financing activities	1,512	5,594
Effect of exchange rate changes on cash and cash equivalents	71	(246)
Net increase (decrease) in cash and cash equivalents	1,162	(8,830)
Cash and cash equivalents, beginning of period	43,039	36,759
Cash and cash equivalents, end of period	$ 44,201	$ 27,929