Valuation And Qualifying Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Allowance For Doubtful Accounts [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of period	$ 6,700	$ 6,072	$ 7,680
Charged to costs and expenses	4,255	2,427	1,179
Deductions	3,439	1,799	2,787
Balance at end of period	7,516	6,700	6,072
Tax Valuation Allowance [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of period	25,979	27,230	27,539
Charged to costs and expenses	0	0	0
Deductions	10,392	1,251	309
Balance at end of period	$ 15,587	$ 25,979	$ 27,230