Condensed Consolidated Statements Of Comprehensive Income - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Revenues	$ 286,466	$ 262,539	$ 568,342	$ 520,961
Costs and expenses:
Cost of revenues	48,753	48,221	99,335	96,574
Sales and marketing	19,757	24,329	39,784	46,711
Research and development	14,288	16,347	31,031	33,499
General and administrative	27,401	24,677	55,158	50,975
Total costs and expenses	110,199	113,574	225,308	227,759
Operating income	176,267	148,965	343,034	293,202
Interest expense	(28,859)	(28,503)	(57,663)	(50,520)
Non-operating income (loss), net	1,709	3,201	4,830	(2,354)
Income before income taxes	149,117	123,663	290,201	240,328
Income tax expense	(35,907)	(30,652)	(69,535)	(59,079)
Net Income	113,210	93,011	220,666	181,249
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Reclassification Adjustment from AOCI, Realized upon Sale or Liquidation, before Tax	(85)	291	(85)	291
Change in unrealized gain on investments, net of tax	851	147	1,786	234
Realized gain on investments, net of tax, included in net income	(1)	(69)	(67)	(73)
Other comprehensive income (loss)	935	(213)	1,804	(130)
Comprehensive Income	$ 114,145	$ 92,798	$ 222,470	$ 181,119
Basic income (loss) per share
Net Income	$ 1.05	$ 0.80	$ 2.03	$ 1.56
Diluted income (loss) per share
Net Income	$ 0.87	$ 0.70	$ 1.68	$ 1.36
Shares used to compute net income per share
Basic	108,067	115,656	108,829	116,394
Diluted	130,588	133,251	131,084	133,546