Condensed Consolidated Statements of Cash Flows (USD $) In Thousands	6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010
Cash flows from operating activities:
Net income	$ 87,672	$ 67,862
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	29,825	30,265
Deferred income tax expense (benefit)	861	(11,895)
Provision for bad debts	141	924
Stock-based compensation expense	10,466	9,160
Excess tax benefits from stock options	(4,903)	(6,553)
Other	113	37
Changes in operating assets and liabilities:
Accounts receivable	9,628	246
Other receivables and current assets	14,754	2,437
Other long-term assets	(391)	3
Accounts payable, accrued expenses and current liabilities	(3,977)	(4,532)
Accrued income taxes	1,735	6,418
Deferred revenue	26,882	26,752
Other long-term liabilities	(9,037)	(1,238)
Net cash provided by operating activities	163,769	119,886
Cash flows from investing activities:
Capital expenditures	(7,605)	(4,419)
Purchases of short-term investments	(234)	(959)
Maturities of short-term investments	141	7,883
Net cash (used in) provided by investing activities	(7,698)	2,505
Cash flows from financing activities:
Principal payments on long-term debt	(10,630)	(55,000)
Principal payments on capital leases	(55)	(153)
Purchase of treasury stock	(12,704)	0
Proceeds from issuance of common stock under Employee Stock Purchase Plan	938	628
Proceeds from exercise of stock options	12,557	11,221
Excess tax benefits from stock options	4,903	6,553
Net cash used in financing activities	(4,991)	(36,751)
Effect of exchange rate fluctuations on cash and cash equivalents	6,153	(6,030)
Net increase in cash and cash equivalents	157,233	79,610
Cash and cash equivalents, beginning of period	472,479	335,878
Cash and cash equivalents, end of period	629,712	415,488
Supplemental disclosures of cash flow information:
Income taxes paid	31,130	35,671
Interest paid	$ 904	$ 1,976