Earnings Per Common Share (Impact Of Company's Stock Price On Assuming Dilution Calculation For The Subordinated Convertible Notes) (Details) - Subordinated Convertible Notes Due 2029	12 Months Ended
	Dec. 31, 2017 $ / shares shares
Changes In Company Stock Price Inclusion Of Additional Shares [Line Items]
Share Price (in dollars per share) | $ / shares	$ 36.75
$31.00
Changes In Company Stock Price Inclusion Of Additional Shares [Line Items]
Share Price (in dollars per share) | $ / shares	$ 31.00
Incremental common shares attributable to contingently issuable shares (in shares)	280,970
$31.00 | Total Treasury Method Incremental Shares
Changes In Company Stock Price Inclusion Of Additional Shares [Line Items]
Incremental common shares attributable to contingently issuable shares (in shares)	280,970
$33.00
Changes In Company Stock Price Inclusion Of Additional Shares [Line Items]
Share Price (in dollars per share) | $ / shares	$ 33.00
Incremental common shares attributable to contingently issuable shares (in shares)	1,120,585
$33.00 | Total Treasury Method Incremental Shares
Changes In Company Stock Price Inclusion Of Additional Shares [Line Items]
Incremental common shares attributable to contingently issuable shares (in shares)	1,120,585
$35.00
Changes In Company Stock Price Inclusion Of Additional Shares [Line Items]
Share Price (in dollars per share) | $ / shares	$ 35.00
Incremental common shares attributable to contingently issuable shares (in shares)	1,864,244
$35.00 | Total Treasury Method Incremental Shares
Changes In Company Stock Price Inclusion Of Additional Shares [Line Items]
Incremental common shares attributable to contingently issuable shares (in shares)	1,864,244
$37.00
Changes In Company Stock Price Inclusion Of Additional Shares [Line Items]
Share Price (in dollars per share) | $ / shares	$ 37.00
Incremental common shares attributable to contingently issuable shares (in shares)	2,527,507
$37.00 | Total Treasury Method Incremental Shares
Changes In Company Stock Price Inclusion Of Additional Shares [Line Items]
Incremental common shares attributable to contingently issuable shares (in shares)	2,527,507
$39.00
Changes In Company Stock Price Inclusion Of Additional Shares [Line Items]
Share Price (in dollars per share) | $ / shares	$ 39.00
Incremental common shares attributable to contingently issuable shares (in shares)	3,122,743
$39.00 | Total Treasury Method Incremental Shares
Changes In Company Stock Price Inclusion Of Additional Shares [Line Items]
Incremental common shares attributable to contingently issuable shares (in shares)	3,122,743