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						9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018
Earnings Per Share [Abstract]
Net income (loss) attributable to common stockholders	$ 42,758			$ 40,979			$ 118,417	$ 117,251
BASIC:
Weighted average common shares outstanding	43,505,332			42,187,077			43,187,847	41,808,017
Net income per common share - basic	$ 0.98			$ 0.97			$ 2.74	$ 2.80
DILUTED:
Weighted average common shares outstanding	43,505,332			42,187,077			43,187,847	41,808,017
Stock options	79,933			98,269			73,924	66,917
Convertible subordinated debentures	275,824			149,153			232,943	57,802
Weighed average dilutive common shares outstanding	43,861,089			42,434,499			43,494,714	41,932,736
Net income per common share - diluted	$ 0.97			$ 0.97			$ 2.72	$ 2.80
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	7,858			615			11,200	31,616
Regular dividends declared per common share	$ 1.05	$ 1.05	$ 1.05	$ 1.00	$ 1.00	$ 1.00	$ 3.15	$ 3.00