Consolidated Statements Of Comprehensive Income - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Statement [Abstract]
Revenues	$ 1,265,052	$ 1,231,661	$ 1,214,969
Costs and expenses:
Cost of revenues	180,177	180,467	192,134
Sales and marketing	36,790	46,637	64,891
Research and development	74,671	60,805	57,884
General and administrative	149,213	137,625	132,668
Total costs and expenses	440,851	425,534	447,577
Operating income	824,201	806,127	767,392
Interest expense	(90,144)	(90,611)	(114,845)
Non-operating income, net	16,187	43,260	76,969
Income from continuing operations before income taxes	750,244	758,776	729,516
Income tax (expense) benefit	64,644	(146,477)	(147,027)
Net income	814,888	612,299	582,489
Other Comprehensive Income (Loss), Net of Tax	(135)	190	130
Comprehensive income	$ 814,753	$ 612,489	$ 582,619
Earnings per share
Earnings Per Share, Basic	$ 7.08	$ 5.17	$ 5.13
Earnings Per Share, Diluted	$ 7.07	$ 5.15	$ 4.75
Shares used to compute net income per share
Basic	115,058	118,513	113,452
Diluted	115,298	118,968	122,661