Shares And Stockholders' Equity (Reconciliation Of The Denominator Calculations Of Basic And Diluted EPS) (Details) - shares	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
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	217,997,297	223,555,299	218,182,118	224,581,848
Shares to cover exercise of outstanding warrants	639,071	694,403	640,929	858,916
Shares to cover non-vested stock	1,475,976	1,426,550	1,534,469	1,551,173
Average stock options outstanding during the period	1,752,403	2,339,558	1,860,997	2,510,344
Assumed acquisition of shares with assumed proceeds from exercising outstanding warrants	(91,876)	(105,156)	(86,482)	(127,696)
Assumed acquisition of shares with assumed proceeds and benefits from exercising stock options (at average market price for the period)	(1,086,798)	(1,464,321)	(1,094,976)	(1,541,738)
Shares repurchaseable from measured but unrecognized stock option expense	(16,356)	(59,959)	(20,467)	(68,519)
Average deferred compensation shares	934,869	927,508	928,466	938,661
Weighted-average shares, as used in diluted calculation	221,604,586	227,313,882	221,945,054	228,702,989