UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015
Operating activities:
Net income	$ 15,070	$ 15,364
Adjustments to reconcile net income to cash provided by operating activities:
Excess tax benefits from exercise or vesting of equity awards	(3,160)	(4,661)
Deferred income taxes	(2,841)	(2,889)
Depreciation and amortization	17,896	17,570
Stock-based compensation expense	30,634	23,005
Foreign currency transaction (gain) loss	(2,764)	4,342
Other non-cash	153	1,129
Change in operating assets and liabilities:
Trade accounts receivable	3,940	21,969
Income taxes receivable and other current assets	(8,737)	(8,670)
Accounts payable and accrued expenses	(16,678)	(4,108)
Deferred revenue	(17,698)	(6,925)
Other long-term assets and liabilities	1,581	(1,198)
Cash provided by operating activities	17,396	54,928
Investing activities:
Purchases of marketable securities	(22,614)	(66,946)
Proceeds from maturities and called marketable securities	21,838	33,916
Sales of marketable securities	62,283	1,915
Payments for acquisitions, net of cash acquired	(49,113)	(1,671)
Investment in property and equipment	(15,253)	(9,950)
Cash used in investing activities	(2,859)	(42,736)
Financing activities:
Issuance of common stock for share-based compensation plans	393	722
Excess tax benefits from exercise or vesting of equity awards	3,160	4,661
Dividend payments to shareholders	(6,883)	(6,896)
Common stock repurchases for tax withholdings for net settlement of equity awards	(10,791)	(7,149)
Common stock repurchases under share repurchase programs	(25,750)	(17,000)
Cash used in financing activities	(39,871)	(25,662)
Effect of exchange rates on cash and cash equivalents	(1,309)	(3,837)
Net decrease in cash and cash equivalents	(26,643)	(17,307)
Cash and cash equivalents, beginning of period	93,026	114,585
Cash and cash equivalents, end of period	$ 66,383	$ 97,278