Earnings and Dividends Per Share (Summary Of Calculation Of Basic And Diluted Earnings Per Share) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
Earnings Per Share [Abstract]
Net income (loss) attributable to common stockholders	$ 39,979		$ 37,839		$ 75,658	$ 76,271
Net income	$ 39,978		$ 37,839		$ 75,657	$ 76,271
BASIC:
Weighted average common shares outstanding	43,232,384		41,704,819		43,029,104	41,618,487
Net income per common share - basic	$ 0.92		$ 0.91		$ 1.76	$ 1.83
DILUTED:
Weighted average common shares outstanding	43,232,384		41,704,819		43,029,104	41,618,487
Stock options	66,145		57,759		70,920	51,241
Convertible subordinated debentures	199,492		24,251		211,503	12,126
Weighed average dilutive common shares outstanding	43,498,021		41,786,829		43,311,527	41,681,854
Net income per common share - diluted	$ 0.92		$ 0.91		$ 1.75	$ 1.83
Incremental shares excluded since anti-dilutive:
Net share effect of stock options with an exercise price in excess of the average market price for our common shares	40,173		33,554		21,227	50,952
Regular dividends declared per common share	$ 1.05	$ 1.05	$ 1.00	$ 1.00	$ 2.10	$ 2.00