Common Stock (Basic And Diluted Earnings Per Share) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended				6 Months Ended		12 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Earnings Per Share [Abstract]
Basic number of common shares outstanding	40,602,343		40,517,713		40,592,693	40,504,526	40,565,007	40,467,231
Dilutive effect of unvested performance awards	93,664		130,086		87,241	113,519	108,137	126,818
Diluted number of common shares outstanding	40,696,007		40,647,799		40,679,934	40,618,045	40,673,144	40,594,049
Net income	$ 26,126	$ 6,089	$ 33,295	$ (6,966)	$ 32,215	$ 26,329	$ 90,201	$ 92,513
Income allocated to participating restricted stock	(95)		(124)		(111)	(98)	(313)	(336)
Net income available to common shareholders, basic	26,031		33,171		32,104	26,231	89,888	92,177
Income reallocated to participating restricted stock	(95)		(124)		(111)	(98)	(313)	(336)
Net income (loss) available to common shareholders, diluted	$ 26,031		$ 33,171		$ 32,104	$ 26,231	$ 89,888	$ 92,177
Earnings Per Share, Basic, Distributed	$ 0.385		$ 0.36		$ 0.745	$ 0.695	$ 1.465	$ 1.365
Earnings (losses) Per Share, Basic, Undistributed	0.255		0.46		0.045	(0.045)	0.755	0.915
Basic net income per common share	0.640		0.82		0.790	0.650	2.220	2.280
Earnings Per Share, Diluted, Distributed	0.385		0.36		0.745	0.695	1.465	1.365
Earnings (losses) Per Share, Diluted, Undistributed	0.255		0.46		0.045	(0.045)	0.745	0.905
Diluted net income per common share	$ 0.640		$ 0.82		$ 0.790	$ 0.650	$ 2.210	$ 2.270