Schedule II Valuation and Qualifying Accounts and Reserves (Details) - SEC Schedule, 12-09, Allowance, Credit Loss - 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	$ 466	$ 759	$ 418
Recoveries added to allowance	631	616	628
Bad debt expense	1,983	2,179	2,456
Losses charged to allowance	(2,546)	(3,088)	(2,743)
Balance at End of Year	$ 534	$ 466	$ 759