Condensed Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Income Statement [Abstract]
Revenues	$ 1,215,877	$ 949,525
Costs and operating expenses:
Cost of revenues	622,430	468,961
Sales and marketing	159,776	128,927
General and administrative	203,157	181,399
Acquisition costs	4,639	3,025
Total costs and operating expenses	990,002	782,312
Income from operations	225,875	167,213
Interest income	4,610	3,092
Interest expense	(126,277)	(111,684)
Other income (expense)	(3,064)	337
Loss on debt extinguishment	(21,491)	(3,503)
Income before income taxes	79,653	55,455
Income tax expense	(16,759)	(13,393)
Net income	$ 62,894	$ 42,062
Earnings per share (EPS):
Basic EPS (in dollars per share)	$ 0.79	$ 0.58
Weighted-average shares for basic EPS (in shares)	79,241	72,773
Diluted EPS (in dollars per share)	$ 0.79	$ 0.57
Weighted-average shares for diluted EPS (in shares)	79,649	73,367
Cash dividends declared (in dollars per share)	$ 2.28	$ 2