Earnings Per Common Share And Share Awards Summary Of Share-Based Award Transactions (Details) - SARs - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Number Of Shares, Outstanding Beginning Balance	28	25
Number Of Shares, SARs granted	0	4
Number Of Shares, SARS exercised	(3)	(1)
Number Of Shares, Outstanding Ending Balance	25	28	25
Number Of Shares, Exercisable as of March 31, 2019	25
Number Of Shares, Unvested as of March 31, 2019	0
Share-based Compensation Arrangement by Share-based Payment Award, SARs, Outstanding, Weighted Average Exercise Price [Roll Forward]
Weighted Average Exercise Price, Outstanding Beginning Balance	$ 110.27	$ 93.40
Weighted Average Exercise Price, SARs granted	0.00	188.71
Weighted Average Exercise Price, SARS exercised	50.50	41.50
Weighted Average Exercise Price, Outstanding Ending Balance	117.30	$ 110.27	$ 93.40
Weighted Average Exercise Price, Exercisable as of March 31, 2019	117.30
Share Based Compensation Arrangement By Share Based Payment Award, Unvested, Weighted Average Exercise Price	$ 0.00
Average Remaining Contractual Term, Outstanding Beginning Balance	3 years 9 months 10 days	3 years 7 months 20 days	3 years 11 months 23 days
Average Remaining Contractual Term, Outstanding Ending Balance	3 years 9 months 10 days	3 years 7 months 20 days	3 years 11 months 23 days
Average Remaining Contractual Term, Exercisable as of March 31, 2019	3 years 9 months 10 days
Average Remaining Contractual Term, Unvested as of March 31, 2019	0 days
Aggregate Intrinsic Value, Outstanding Beginning Balance	$ 2,019	$ 2,624
Aggregate Intrinsic Value, Outstanding Ending Balance	1,331	$ 2,019	$ 2,624
Aggregate Intrinsic Value, Exercisable as of March 31, 2019	1,331
Aggregate Intrinsic Value, Unvested as of March 31, 2019	$ 0