Organization and Significant Accounting Policies - Recent and Recently Adopted Accounting Pronouncements (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Recently Adopted Accounting Pronouncements
Net operating revenues	$ 1,114,401	$ 1,097,166	$ 1,120,675	$ 1,111,361	$ 1,046,265	$ 1,053,795	$ 1,097,631	$ 1,088,330	$ 4,443,603	$ 4,286,021	$ 3,742,736
Bad debt expense									79,491	69,093	59,372
Total current assets	920,826				762,903				920,826	762,903
Other assets	184,418				173,944				184,418	173,944
Total assets	5,127,166				4,920,626				5,127,166	4,920,626	$ 4,388,678
Non-current deferred tax liability	124,917				199,078				124,917	199,078
Total liabilities	3,553,744				3,592,566				3,553,744	3,592,566
Total liabilities and equity	$ 5,127,166				4,920,626				5,127,166	4,920,626
Accounting Standards Update 2014-09 | Pro Forma
Recently Adopted Accounting Pronouncements
Net operating revenues									4,365,245	4,217,460
Bad debt expense									$ 1,133	532
Accounting Standards Update 2015-17 | Scenario, Previously Reported
Recently Adopted Accounting Pronouncements
Current deferred tax asset					45,165					45,165
Total current assets					808,068					808,068
Other assets					152,548					152,548
Total assets					4,944,395					4,944,395
Non-current deferred tax liability					222,847					222,847
Total liabilities					3,616,335					3,616,335
Total liabilities and equity					$ 4,944,395					$ 4,944,395