Condensed Consolidated Statements Of Comprehensive Income - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Revenues	$ 305,777	$ 292,428	$ 907,517	$ 869,594
Costs and expenses:
Cost of revenues	48,249	47,333	143,766	145,646
Sales and marketing	13,868	18,667	47,712	56,463
Research and development	13,712	12,715	42,842	39,569
General and administrative	34,951	32,654	99,771	96,626
Total costs and expenses	110,780	111,369	334,091	338,304
Operating income	194,997	181,059	573,426	531,290
Interest expense	(22,631)	(37,756)	(92,211)	(95,869)
Non-operating income (loss), net	5,935	6,241	14,399	21,544
Income before income taxes	178,301	149,544	495,614	456,965
Income tax expense	(40,621)	(34,645)	(95,320)	(102,554)
Net Income	137,680	114,899	400,294	354,411
Other comprehensive income (loss)	(322)	(264)	(62)	299
Comprehensive Income	$ 137,358	$ 114,635	$ 400,232	$ 354,710
Basic income (loss) per share
Net Income	$ 1.13	$ 1.15	$ 3.60	$ 3.51
Diluted income (loss) per share
Net Income	$ 1.13	$ 0.93	$ 3.25	$ 2.85
Shares used to compute net income per share
Basic	121,682	99,614	111,046	101,036
Diluted	122,261	124,074	123,079	124,162