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, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Earnings Per Share [Abstract]
Net income attributable to common stockholders	$ 41,188	$ 33,032	$ 44,595	$ 32,725	$ 54,397	$ 33,600	$ 31,182	$ 29,683	$ 151,540	$ 148,862	$ 101,609
BASIC:
Weighted Average Number of Shares Outstanding, Basic	39,847,860	39,283,919	38,520,221	38,401,647	37,727,868	37,566,221	37,566,221	37,558,067	39,013,412	37,604,594	33,375,966
Net income per common share attributable to common stockholders	$ 1.03	$ 0.84	$ 1.16	$ 0.85	$ 1.44	$ 0.89	$ 0.83	$ 0.79	$ 3.88	$ 3.96	$ 3.04
DILUTED:
Weighted average common shares outstanding, diluted									39,013,412	37,604,594	33,375,966
Stock options, diluted									52,497	34,842	40,048
Convertible subordinated debentures									89,471	4,735	0
Average dilutive common shares outstanding	39,993,445	39,651,900	38,561,384	38,414,791	37,741,162	37,583,141	37,607,117	37,645,265	39,155,380	37,644,171	33,416,014
Net income per common share attributable to common stockholders	$ 1.03	$ 0.83	$ 1.16	$ 0.85	$ 1.44	$ 0.89	$ 0.83	$ 0.79	$ 3.87	$ 3.95	$ 3.04
Net share effect of anti-dilutive stock options									6,366	51,603	13,831
Common Stock, Dividends, Per Share, Declared, Regular									$ 3.60	$ 3.40	$ 3.08