UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017
Operating activities:
Net income	[1]	$ 1,791	$ 56,665
Adjustments to reconcile net income to cash provided by operating activities:
Change in operating assets and liabilities, net	[1]	30,158	(14,874)
Stock-based compensation expense	[1]	31,165	26,440
Depreciation and amortization of intangible assets	[1]	12,474	12,356
Other non-cash	[1]	(156)	5,182
Cash provided by operating activities	[1]	75,432	85,769
Investing activities:
Purchases of investments	[1]	(51,395)	(16,656)
Proceeds from maturities and called investments	[1]	11,546	20,824
Other	[1]	(6,520)	(5,327)
Cash used in investing activities	[1]	(46,369)	(1,159)
Financing activities:
Dividend payments to shareholders	[1]	(4,702)	(4,613)
Common stock repurchases	[1]	(41,123)	(30,247)
Cash used in financing activities	[1]	(45,825)	(34,860)
Effect of exchange rates on cash and cash equivalents	[1]	(1,226)	1,282
Net (decrease)/increase in cash and cash equivalents	[1]	(17,988)	51,032
Cash and cash equivalents, beginning of period	[1]	162,279	70,594
Cash and cash equivalents, end of period	[1]	$ 144,291	$ 121,626

[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.