Schedule II - Valuation and Qualifying Accounts (Valuation and Qualifying Accounts) (Details) - Allowance for doubtful accounts [Member] - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Valuation and Qualifying Accounts
Balance at beginning of period		$ 12,717	$ 12,040	$ 9,637
Additions - charged to costs and expenses		9,475	8,598	9,587
Additions - charged to other accounts - describe		0	0	0
Deductions - describe	[1]	8,954	7,921	7,184
Balance at end of period		$ 13,238	$ 12,717	$ 12,040

[1] Uncollectable accounts written off.