UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Operating activities:
Net income	$ 38,427	$ 14,936
Adjustments to reconcile net income to cash provided by operating activities:
Deferred income taxes	(465)	(1,190)
Depreciation and amortization	12,356	11,675
Stock-based compensation expense	26,440	19,816
Foreign currency transaction loss (gain)	241	(1,682)
Other non-cash	(408)	4,576
Change in operating assets and liabilities:
Trade accounts receivable	52,966	10,853
Income taxes receivable and other current assets	(14,294)	(18,349)
Accounts payable and accrued expenses	(17,734)	(19,259)
Deferred revenue	(11,890)	(11,222)
Other long-term assets and liabilities	130	1,415
Cash provided by operating activities	85,769	11,569
Investing activities:
Purchases of marketable securities	(16,656)	(20,942)
Proceeds from maturities and called marketable securities	20,824	21,139
Sales of marketable securities		52,483
Payments for acquisitions, net of cash acquired	(290)	(49,113)
Investment in property and equipment	(5,037)	(11,497)
Cash used in investing activities	(1,159)	(7,930)
Financing activities:
Dividend payments to shareholders	(4,613)	(4,592)
Common stock repurchases for tax withholdings for net settlement of equity awards	(27,261)	(7,849)
Common stock repurchases under share repurchase programs	(2,986)	(19,225)
Cash used in financing activities	(34,860)	(31,666)
Effect of exchange rates on cash and cash equivalents	1,282	(738)
Net increase (decrease) in cash and cash equivalents	51,032	(28,765)
Cash and cash equivalents, beginning of period	70,594	93,026
Cash and cash equivalents, end of period	$ 121,626	$ 64,261