UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Operating activities:
Net income	$ 27,021	$ 10,400
Adjustments to reconcile net income to cash provided by operating activities:
Deferred income taxes	727	650
Depreciation and amortization	6,088	5,466
Stock-based compensation expense	12,508	8,935
Foreign currency transaction gain	(676)	(1,376)
Other non-cash	(379)	2,712
Change in operating assets and liabilities:
Trade accounts receivable	3,383	6,697
Income taxes receivable and other current assets	(4,382)	(201)
Accounts payable and accrued expenses	(21,193)	(24,822)
Deferred revenue	9,412	1,129
Other long-term assets and liabilities	(65)	450
Cash provided by operating activities	32,444	10,040
Investing activities:
Purchases of marketable securities	(3,322)	(8,193)
Proceeds from maturities and called marketable securities	2,300	15,890
Sales of marketable securities		6,179
Payments for acquisitions, net of cash acquired	(290)	(255)
Investment in property and equipment	(2,415)	(4,251)
Cash (used in) provided by investing activities	(3,727)	9,370
Financing activities:
Issuance of common stock for share-based compensation plans	68	44
Dividend payments to shareholders	(2,298)	(2,297)
Common stock repurchases for tax withholdings for net settlement of equity awards and under share repurchase programs	(13,764)	(17,569)
Cash used in financing activities	(15,994)	(19,822)
Effect of exchange rates on cash and cash equivalents	521	(434)
Net increase (decrease) in cash and cash equivalents	13,244	(846)
Cash and cash equivalents, beginning of period	70,594	93,026
Cash and cash equivalents, end of period	$ 83,838	$ 92,180