Condensed Consolidated Statements Of Comprehensive Income - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Income Statement [Abstract]
Revenues	$ 262,539	$ 250,382	$ 520,961	$ 499,178
Costs and expenses:
Cost of revenues	48,221	45,989	96,574	94,015
Sales and marketing	24,329	23,651	46,711	43,940
Research and development	16,347	15,694	33,499	34,133
General and administrative	24,677	21,927	50,975	44,384
Total costs and expenses	113,574	107,261	227,759	216,472
Operating income	148,965	143,121	293,202	282,706
Interest expense	(28,503)	(21,490)	(50,520)	(42,875)
Non-operating income (loss), net	3,201	4,994	(2,354)	11,510
Income before income taxes	123,663	126,625	240,328	251,341
Income tax expense	(30,652)	(26,449)	(59,079)	(56,742)
Net Income	93,011	100,176	181,249	194,599
Realized foreign currency translation adjustments, included in net income	(291)	0	(291)	0
Change in unrealized gain on investments, net of tax	147	(33)	234	(25)
Realized gain on investments, net of tax, included in net income	(69)	(2)	(73)	3
Other comprehensive income (loss)	(213)	(35)	(130)	(22)
Comprehensive Income	$ 92,798	$ 100,141	$ 181,119	$ 194,577
Basic income (loss) per share
Continuing operations	$ 0.80	$ 0.77	$ 1.56	$ 1.48
Diluted income (loss) per share
Continuing operations	$ 0.70	$ 0.71	$ 1.36	$ 1.34
Shares used to compute net income per share
Basic	115,656	129,350	116,394	131,372
Diluted	133,251	141,142	133,546	144,861