Condensed Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Income Statement [Abstract]
Revenues	$ 1,283,751	$ 1,152,261	$ 3,761,571	$ 3,168,207
Costs and operating expenses:
Cost of revenues	660,309	582,360	1,934,540	1,573,524
Sales and marketing	157,920	157,619	471,898	428,112
General and administrative	206,902	185,336	620,548	558,090
Acquisition costs	(1,120)	2,083	33,932	31,510
Gain on asset sales	6,013	0	6,013	0
Total costs and operating expenses	1,017,998	927,398	3,054,905	2,591,236
Income from operations	265,753	224,863	706,666	576,971
Interest income	2,912	2,291	11,480	9,820
Interest expense	(130,566)	(121,828)	(391,516)	(352,554)
Other income (expense)	3,744	(1,076)	9,546	545
Gain (loss) on debt extinguishment	1,492	(22,156)	(39,214)	(42,103)
Income before income taxes	143,335	82,094	296,962	192,679
Income tax expense	(18,510)	(2,194)	(41,625)	(24,912)
Net income	$ 124,825	$ 79,900	$ 255,337	$ 167,767
Earnings per share (EPS):
Basic EPS (in dollars per share)	$ 1.56	$ 1.02	$ 3.21	$ 2.20
Weighted-average shares for basic EPS (in shares)	79,872	78,055	79,533	76,283
Diluted EPS (in dollars per share)	$ 1.55	$ 1.02	$ 3.19	$ 2.18
Weighted-average shares for diluted EPS (in shares)	80,283	78,719	79,956	76,948
Cash dividends declared (in dollars per share)	$ 2.28	$ 2.00	$ 6.84	$ 6.00