Consolidated Statements Of Comprehensive Income - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Statement [Abstract]
Revenues	$ 1,059,366	$ 1,010,117	$ 965,087
Costs and expenses:
Cost of revenues	192,788	188,425	187,013
Sales and marketing	90,184	92,001	89,337
Research and development	63,718	67,777	70,297
General and administrative	106,730	97,487	90,208
Total costs and expenses	453,420	445,690	436,855
Operating income	605,946	564,427	528,232
Interest expense	(107,631)	(85,994)	(74,761)
Non-operating income, net	(10,665)	4,878	3,300
Income from continuing operations before income taxes	487,650	483,311	456,771
Income tax (expense) benefit	(112,414)	(128,051)	87,679
Net income	375,236	355,260	544,450
Realized foreign currency translation adjustments, included in net income	(291)	0	81
Change in unrealized gain on investments, net of tax	(519)	84	(369)
Realized gain on investments, net of tax, included in net income	(185)	3	(2,409)
Other comprehensive income (loss)	(995)	87	(2,697)
Comprehensive income	$ 374,241	$ 355,347	$ 541,753
Earnings per share
Earnings Per Share, Basic	$ 3.29	$ 2.80	$ 3.77
Earnings Per Share, Diluted	$ 2.82	$ 2.52	$ 3.49
Shares used to compute net income per share
Basic	114,155	126,710	144,591
Diluted	133,031	140,895	155,786