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, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Earnings Per Share [Abstract]
Net income (loss) attributable to common stockholders	$ 37,839	$ 38,245	$ 76,271	$ 82,475
BASIC:
Weighted Average Number of Shares Outstanding, Basic	41,704,819	40,982,244	41,618,487	40,468,024
Income (Loss) from Continuing Operations, Per Basic Share	$ 0.91	$ 0.93	$ 1.83	$ 2.04
DILUTED:
Weighted average common shares outstanding, diluted	41,704,819	40,982,244	41,618,487	40,468,024
Stock options, diluted	57,759	66,137	51,241	63,901
Incremental Common Shares Attributable to Dilutive Effect of Conversion of Debt Securities	24,251	196,792	12,126	147,420
Average dilutive common shares outstanding	41,786,829	41,245,173	41,681,854	40,679,345
Income (Loss) from Continuing Operations, Per Diluted Share	$ 0.91	$ 0.93	$ 1.83	$ 2.03
Incremental shares excluded since anti-dilutive:
Stock options with an exercise price in excess of the market price for our common shares	33,554	11,015	50,952	9,736
Common Stock Dividends, Per Share, Declared, Regular	$ 1.00	$ 0.95	$ 2.00	$ 1.90