Earnings Per Common Share And Share Awards Summary Of Share-Based Award Transactions (Details) - SARs - USD ($) $ / shares in Units, $ in Thousands	6 Months Ended		12 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Number Of Shares, Outstanding Beginning Balance	25,000	25,000	25,000
Number Of Shares, SARs granted	4,000	4,000	4,000
Number Of Shares, SARS exercised	(1,000)		(4,000)
Number Of Shares, Outstanding Ending Balance	28,000		25,000	25,000
Number Of Shares, Exercisable as of June 30, 2018	25,000
Number Of Shares, Unvested as of June 30, 2018	3,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Roll Forward]
Weighted Average Exercise Price, Outstanding Beginning Balance	$ 93.40	$ 65.85	$ 65.85
Weighted Average Exercise Price, SARs granted	188.71		192.71
Weighted Average Exercise Price, SARS exercised	41.50		36.38
Weighted Average Exercise Price, Outstanding Ending Balance	110.27		$ 93.40	$ 65.85
Weighted Average Exercise Price, Exercisable as of June 30, 2018	$ 99.73
Average Remaining Contractual Term, Outstanding Beginning Balance	4 years 1 month 24 days		3 years 11 months 23 days	3 years 10 months 6 days
Average Remaining Contractual Term, Outstanding Ending Balance	4 years 1 month 24 days		3 years 11 months 23 days	3 years 10 months 6 days
Average Remaining Contractual Term, Exercisable as of June 30, 2018	3 years 9 months 10 days
Aggregate Intrinsic Value, Outstanding Beginning Balance	$ 837	$ 837	$ 837
Aggregate Intrinsic Value, Outstanding Ending Balance	2,175		$ 837	$ 837
Aggregate Intrinsic Value, Exercisable as of June 30, 2018	$ 2,175
Share Based Compensation Arrangement By Share Based Payment Award, Unvested, Weighted Average Exercise Price	$ 188.71
Average Remaining Contractual Term, Unvested as of June 30, 2018	6 years 10 months 17 days
Aggregate Intrinsic Value, Unvested as of June 30, 2018	$ 0