CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014
Operating activities:
Net income	$ 15,364	$ 13,151
Adjustments to reconcile net income to cash provided by operating activities:
Excess tax benefits from exercise or vesting of equity awards	(4,661)	(3,754)
Deferred income taxes	(2,889)	(1,845)
Depreciation and amortization	17,570	17,167
Stock-based compensation expense	23,005	13,721
Foreign currency transaction loss	4,342	2,527
Other non-cash items	1,129	939
Change in operating assets and liabilities:
Trade accounts receivable	21,969	59,049
Income taxes receivable and other current assets	(8,670)	(3,839)
Accounts payable and accrued expenses	(4,108)	(1,448)
Deferred revenue	(6,925)	4,287
Other long-term assets and liabilities	(1,198)	(1,688)
Cash provided by operating activities	54,928	98,267
Investing activities:
Purchases of marketable securities	(66,946)	(36,232)
Proceeds from maturities and called marketable securities	33,916	22,156
Sale of marketable securities	1,915
Payments for acquisitions	(1,671)	(2,600)
Investment in property and equipment	(9,950)	(5,809)
Cash used in investing activities	(42,736)	(22,485)
Financing activities:
Issuance of common stock for share-based compensation plans	722	629
Excess tax benefits from exercise or vesting of equity awards	4,661	3,754
Dividend payments to shareholders	(6,896)	(4,581)
Common stock repurchases for tax withholdings for net settlement of equity awards	(7,149)	(4,939)
Common stock repurchases under share repurchase programs	(17,000)	(12,266)
Cash used in financing activities	(25,662)	(17,403)
Effect of exchange rates on cash and cash equivalents	(3,837)	(2,065)
Net (decrease) increase in cash and cash equivalents	(17,307)	56,314
Cash and cash equivalents, beginning of period	114,585	80,231
Cash and cash equivalents, end of period	$ 97,278	$ 136,545