Shares And Stockholders' Equity (Reconciliation Of The Denominator Calculations Of Basic And Diluted EPS) (Details) - shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Reconciliation of the denominator (number of shares) in the calculations of basic and diluted earnings (loss) per common share
Weighted-average shares, as used in basic calculation	193,610,225	200,608,737	215,936,448
Shares to cover exercise of outstanding warrants		58,765	568,602
Shares to cover non-vested stock	687,240	973,901	1,534,142
Average stock options outstanding during the period	746,742	1,507,049	1,739,029
Assumed acquisition of shares with assumed proceeds from exercising outstanding warrants		(9,594)	(81,260)
Assumed acquisition of shares with assumed proceeds and benefits from exercising stock options (at average market price for the period)	(576,582)	(1,033,507)	(1,074,406)
Shares repurchasable from measured but unrecognized stock option expense	(2,445)	(217)	(14,600)
Average deferred compensation shares			944,151
Weighted-average shares, as used in diluted calculation	194,465,180	202,105,134	219,552,106