Condensed Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012
Operating activities:
Net income	$ 22,482	$ 1,459
Adjustments to reconcile net income to cash provided by operating activities:
Excess tax benefits from exercise or vesting of equity awards	(2,670)	(3,161)
Deferred income taxes	(537)	(511)
Depreciation and amortization	14,173	13,986
Stock-based compensation expense	9,713	8,622
Foreign currency transaction loss (gain)	1,666	(337)
Other non-cash items	2,736	4,021
Change in operating assets and liabilities:
Trade accounts receivable	42,611	18,938
Income taxes receivable and other current assets	2,599	(1,468)
Accounts payable and accrued expenses	(5,762)	(20,491)
Deferred revenue	(3,836)	2,747
Other long-term assets and liabilities	260	5,279
Cash provided by operating activities	83,435	29,084
Investing activities:
Purchase of marketable securities	(56,645)	(13,336)
Matured and called marketable securities	21,129	18,465
Investment in property and equipment	(4,158)	(21,875)
Cash used in investing activities	(39,674)	(16,746)
Financing activities:
Issuance of common stock for share-based compensation plans	970	753
Excess tax benefits from exercise or vesting of equity awards	2,670	3,161
Dividend payments to shareholders	(2,281)	(3,404)
Common stock repurchases for tax withholdings for net settlement of equity awards	(4,123)	(3,650)
Common stock repurchases under share repurchase programs	(9,178)	(3,910)
Cash used in financing activities	(11,942)	(7,050)
Effect of exchange rate on cash and cash equivalents	(517)	596
Net increase in cash and cash equivalents	31,302	5,884
Cash and cash equivalents, beginning of period	77,525	60,353
Cash and cash equivalents, end of period	$ 108,827	$ 66,237