UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017
Operating activities:
Net (loss) income	[1]	$ (5,796)	$ 57,953
Adjustment to reconcile net (loss) income to cash provided by operating activities:
Change in operating assets and liabilities, net	[1]	8,698	(15,455)
Stock-based compensation expense	[1]	47,573	39,929
Amortization of intangible assets and depreciation	[1]	18,692	18,703
Other non-cash	[1]	(2,079)	12,796
Cash provided by operating activities	[1]	67,088	113,926
Investing activities:
Purchases of investments	[1]	(68,177)	(25,687)
Proceeds from maturities and called investments	[1]	26,456	23,124
Other	[1]	(7,874)	(9,403)
Cash used in investing activities	[1]	(49,595)	(11,966)
Financing activities:
Dividend payments to shareholders	[1]	(7,067)	(6,941)
Common stock repurchases	[1]	(64,597)	(37,099)
Cash used in financing activities	[1]	(71,664)	(44,040)
Effect of exchange rates on cash and cash equivalents	[1]	(1,913)	2,054
Net (decrease) increase in cash and cash equivalents	[1]	(56,084)	59,974
Cash and cash equivalents, beginning of period	[1]	162,279	70,594
Cash and cash equivalents, end of period	[1]	$ 106,195	$ 130,568

[1] On January 1, 2018, the Company adopted the ASC 606 revenue recognition standard and has adjusted prior periods to conform. See Note 2. "New Accounting Pronouncements" for additional information.