SEC Schedule II Valuation and Qualifying Accounts (Details) - Allowance For Doubtful Accounts - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Year	$ 6,480	$ 8,621	$ 10,075
Additions Charged Against Operations	1,910	26	1,827
Uncollectible Accounts Written-off	(2,592)	(2,167)	(3,281)
Balance at End of Year	$ 5,798	$ 6,480	$ 8,621