Schedule II Valuation and Qualifying Accounts (Details) - Reserve for Uncollectible Accounts [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Movement in Reserve [Roll Forward]
Balance at beginning of year	$ 325,000	$ 320,000	$ 305,000
Charged to cost and expenses	292,248	322,499	290,886
Recoveries	40,681	44,071	36,369
Deductions	342,929	361,570	312,255
Balance at end of year	$ 315,000	$ 325,000	$ 320,000