Common Stock (Basic And Diluted Earnings Per Share) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
Earnings Per Share [Abstract]
Basic number of common shares outstanding	40,582,936	40,491,194	40,543,986	40,440,189
Dilutive effect of unvested performance awards	80,817	0	117,242	123,436
Diluted number of common shares outstanding	40,663,753	40,491,194	40,661,228	40,563,625
Net income (loss)	$ 6,089	$ (6,966)	$ 97,370	$ 95,285
Income allocated to participating restricted stock	(47)	(48)	(340)	(353)
Net income (loss) available to common shareholders, basic	6,042	(7,014)	97,030	94,932
Income reallocated to participating restricted stock	(47)	(48)	(339)	(353)
Net income (loss) available to common shareholders, diluted	$ 6,042	$ (7,014)	$ 97,031	$ 94,932
Earnings Per Share, Basic, Distributed	$ 0.36	$ 0.335	$ 1.44	$ 1.34
Earnings (losses) Per Share, Basic, Undistributed	(0.21)	(0.505)	0.95	1.01
Basic net income (loss) per common share	0.15	(0.170)	2.39	2.35
Earnings Per Share, Diluted, Distributed	0.36	0.335	1.44	1.34
Earnings (losses) Per Share, Diluted, Undistributed	(0.21)	(0.505)	0.95	1.00
Diluted net income (loss) per common share	$ 0.15	$ (0.170)	$ 2.39	$ 2.34