Valuation and Qualifying Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Allowance for uncollectible accounts
Balance at Beginning of Period	$ 21,775	$ 19,846	$ 17,702
Additions Charged to Costs and Expenses	8,306	8,401	6,248
Additions Charged to Other Accounts	0	0	0
Write-offs	(5,509)	(6,098)	(6,129)
Other	(1,132)	(374)	2,025
Balance at End of Period	$ 23,440	$ 21,775	$ 19,846