Consolidated Statements Of Comprehensive Income - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Statement [Abstract]
Revenues	$ 1,231,661	$ 1,214,969	$ 1,165,095
Costs and expenses:
Cost of revenues	180,467	192,134	193,326
Sales and marketing	46,637	64,891	81,951
Research and development	60,805	57,884	52,342
General and administrative	137,625	132,668	129,754
Total costs and expenses	425,534	447,577	457,373
Operating income	806,127	767,392	707,722
Interest expense	(90,611)	(114,845)	(136,336)
Non-operating income, net	43,260	76,969	27,626
Income from continuing operations before income taxes	758,776	729,516	599,012
Income tax (expense) benefit	(146,477)	(147,027)	(141,764)
Net income	612,299	582,489	457,248
Other comprehensive income (loss)	190	130	512
Comprehensive income	$ 612,489	$ 582,619	$ 457,760
Earnings per share
Earnings Per Share, Basic	$ 5.17	$ 5.13	$ 4.56
Earnings Per Share, Diluted	$ 5.15	$ 4.75	$ 3.68
Shares used to compute net income per share
Basic	118,513	113,452	100,325
Diluted	118,968	122,661	124,180