Consolidated Statements Of Comprehensive Income - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Statement [Abstract]
Revenues	$ 1,142,167	$ 1,059,366	$ 1,010,117
Costs and expenses:
Cost of revenues	198,242	192,788	188,425
Sales and marketing	80,250	90,184	92,001
Research and development	59,100	63,718	67,777
General and administrative	118,003	106,730	97,487
Total costs and expenses	455,595	453,420	445,690
Operating income	686,572	605,946	564,427
Interest expense	(115,564)	(107,631)	(85,994)
Non-operating income, net	10,165	(10,665)	4,878
Income from continuing operations before income taxes	581,173	487,650	483,311
Income tax (expense) benefit	(140,528)	(112,414)	(128,051)
Net income	440,645	375,236	355,260
Realized foreign currency translation adjustments, included in net income	85	(291)	0
Change in unrealized gain on investments, net of tax	533	(519)	84
Realized gain on investments, net of tax, included in net income	(78)	(185)	3
Other comprehensive income (loss)	540	(995)	87
Comprehensive income	$ 441,185	$ 374,241	$ 355,347
Earnings per share
Earnings Per Share, Basic	$ 4.12	$ 3.29	$ 2.80
Earnings Per Share, Diluted	$ 3.42	$ 2.82	$ 2.52
Shares used to compute net income per share
Basic	107,001	114,155	126,710
Diluted	128,833	133,031	140,895