Common Stock (Basic And Diluted Earnings Per Share) (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Class of Stock Disclosures [Abstract]
Basic number of common shares outstanding	40,213,741	40,132,250	40,181,367	40,107,555	40,169,801	40,084,525
Dilutive effect of unvested performance awards	51,069	0	27,634	16,071	20,726	28,122
Dilutive effect of stock options					0	2,274
Diluted number of common shares outstanding	40,264,810	40,132,250	40,209,001	40,123,626	40,190,527	40,114,921
Net income	$ 52,476	$ 50,565	$ 87,187	$ 87,392	$ 88,378	$ 92,211
Income allocated to participating restricted stock	(175)	(150)	(293)	(249)	(285)	(253)
Net income available to common shareholders, basic	52,301	50,415	86,894	87,143	88,093	91,958
Income reallocated to participating restricted stock	(175)	(150)	(293)	(249)	(285)	(253)
Net income available to common shareholders, diluted	$ 52,301	$ 50,415	$ 86,894	$ 87,143	$ 88,093	$ 91,958
Earnings Per Share, Basic, Distributed	$ 0.280	$ 0.265	$ 0.825	$ 0.780	$ 1.090	$ 1.030
Earnings Per Share, Basic, Undistributed	$ 1.020	$ 0.995	$ 1.335	$ 1.390	$ 1.100	$ 1.260
Basic net income per common share	$ 1.300	$ 1.260	$ 2.160	$ 2.170	$ 2.190	$ 2.290
Earnings Per Share, Diluted, Distributed	$ 0.280	$ 0.265	$ 0.825	$ 0.780	$ 1.090	$ 1.030
Earnings Per Sare, Diluted, Undistributed	$ 1.020	$ 0.995	$ 1.335	$ 1.390	$ 1.100	$ 1.260
Diluted net income per common share	$ 1.300	$ 1.260	$ 2.160	$ 2.170	$ 2.190	$ 2.290