Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Statement [Abstract]
Revenues	$ 5,071,654	$ 4,368,428	$ 3,611,989
Costs and operating expenses:
Cost of revenues	2,605,475	2,193,149	1,820,870
Sales and marketing	633,702	581,724	438,742
General and administrative	826,694	745,906	694,561
Acquisition costs	34,413	38,635	64,195
Impairment charges	0	0	7,698
Gain on asset sales	(6,013)	0	(32,816)
Total costs and operating expenses	4,094,271	3,559,414	2,993,250
Income from operations	977,383	809,014	618,739
Interest income	14,482	13,075	3,476
Interest expense	(521,494)	(478,698)	(392,156)
Other income (expense)	14,044	9,213	(57,924)
Loss on debt extinguishment	(51,377)	(65,772)	(12,276)
Income from continuing operations before income taxes	433,038	286,832	159,859
Income tax expense	(67,679)	(53,850)	(45,451)
Net income from continuing operations	365,359	232,982	114,408
Net income from discontinued operations, net of tax	0	0	12,392
Net income	$ 365,359	$ 232,982	$ 126,800
Earnings per share (EPS):
Basic EPS from continuing operations (in dollars per share)	$ 4.58	$ 3.03	$ 1.63
Basic EPS of discontinued operations (in dollars per share)	0.00	0.00	0.18
Basic EPS (in dollars per share)	$ 4.58	$ 3.03	$ 1.81
Weighted-average shares	79,779	76,854	70,117
Dilutive EPS from continuing operations (in dollars per share)	$ 4.56	$ 3.00	$ 1.62
Dilutive EPS from discontinued operations (in dollars per share)	0.00	0.00	0.17
Diluted EPS (in dollars per share)	$ 4.56	$ 3.00	$ 1.79
Weighted-average shares	80,197	77,535	70,816
Cash dividends declared per common share (in dollars per share)	$ 9.12	$ 8.00	$ 7.00