Condensed Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Income Statement [Abstract]
Revenues	$ 1,261,943	$ 1,066,421	$ 2,477,820	$ 2,015,946
Costs and operating expenses:
Cost of revenues	651,801	522,203	1,274,231	991,164
Sales and marketing	154,202	141,566	313,978	270,493
General and administrative	210,489	191,355	413,646	372,754
Acquisition costs	30,413	26,402	35,052	29,427
Total costs and operating expenses	1,046,905	881,526	2,036,907	1,663,838
Income from operations	215,038	184,895	440,913	352,108
Interest income	3,958	4,437	8,568	7,529
Interest expense	(134,673)	(119,042)	(260,950)	(230,726)
Other income (expense)	8,866	1,284	5,802	1,621
Loss on debt extinguishment	(19,215)	(16,444)	(40,706)	(19,947)
Income before income taxes	73,974	55,130	153,627	110,585
Income tax expense	(6,356)	(9,325)	(23,115)	(22,718)
Net income	$ 67,618	$ 45,805	$ 130,512	$ 87,867
Earnings per share (EPS):
Basic EPS (in dollars per share)	$ 0.85	$ 0.59	$ 1.64	$ 1.17
Weighted-average shares for basic EPS (in shares)	79,479	77,923	79,361	75,383
Diluted EPS (in dollars per share)	$ 0.85	$ 0.58	$ 1.64	$ 1.16
Weighted-average shares for diluted EPS (in shares)	79,752	78,508	79,746	76,008
Cash dividends declared (in dollars per share)	$ 2.28	$ 2.00	$ 4.56	$ 4.00