Earnings Per Common Share (Schedule Of Net Income (Loss) Per Common Share) (Details) - USD ($)	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Earnings Per Common Share [Abstract]
Net income (loss)	$ 341,862,000	$ 16,612,000
Less: dividends declared-common shares and nonvested common shares	(62,229,000)	(63,277,000)
Undistributed earnings	$ 279,633,000	$ (46,666,000)
Percentage allocated to common shareholders	98.70%	98.70%
Net income (loss) available to common stockholders, total	$ 276,031,000	$ (46,082,000)
Add: dividends declared-common shareholders	61,415,000	62,488,000
Numerator for basic and diluted earnings per common share	$ 337,446,000	$ 16,406,000
Denominator for basic earnings per weighted-average common shares	39,543,000	40,204,000
Effect of dilutive securities: Options	54,000	92,000
Denominator for diluted earnings per adjusted weighted-average common shares	39,597,000	40,296,000
Per common share net income (loss)
Basic	$ 8.53	$ 0.41
Diluted	$ 8.52	$ 0.41
Basic weighted-average common shares outstanding	39,543,000	40,204,000
Basic weighted-average common shares outstanding and nonvested common shares expected to vest	40,059,000	40,713,000