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								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Earnings Per Share [Abstract]
Net income attributable to common stockholders	$ 37,140	$ 42,595	$ 44,368	$ 61,023	$ 42,040	$ 42,758	$ 39,979	$ 35,679	$ 185,126	$ 160,456	$ 154,333
BASIC:
Weighted Average Number of Shares Outstanding, Basic	44,859,894	44,661,650	44,650,002	44,613,593	44,107,770	43,505,332	43,232,384	42,825,824	44,696,285	43,417,828	41,943,873
Net income per common share attributable to common stockholders	$ 0.83	$ 0.95	$ 0.99	$ 1.37	$ 0.95	$ 0.98	$ 0.92	$ 0.83	$ 4.14	$ 3.70	$ 3.68
DILUTED:
Weighted average common shares outstanding, diluted									44,696,285	43,417,828	41,943,873
Stock options, diluted									1,719	75,196	67,735
Convertible subordinated debentures									0	210,224	80,123
Average dilutive common shares outstanding	44,861,469	44,662,403	44,650,002	44,618,139	44,328,847	43,861,089	43,498,021	43,125,032	44,698,004	43,703,248	42,091,731
Net income per common share attributable to common stockholders	$ 0.83	$ 0.95	$ 0.99	$ 1.37	$ 0.95	$ 0.97	$ 0.92	$ 0.83	$ 4.14	$ 3.67	$ 3.67
Incremental shares excluded since anti-dilutive:
Stock options with an exercise price in excess of the market price for our common shares									390,596	4,678	518
Common Stock, Dividends, Per Share, Declared									$ 4.41	$ 4.20	$ 4.00