Common Stock (Basic And Diluted Earnings Per Share) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017
Earnings Per Share [Abstract]
Basic number of common shares outstanding	40,491,194	40,387,235	40,440,189	40,366,024
Dilutive effect of unvested performance awards	0	0	123,436	69,665
Diluted number of common shares outstanding	40,491,194	40,387,235	40,563,625	40,435,689
Net income (loss)	$ (6,966)	$ (3,989)	$ 95,285	$ 98,587
Income allocated to participating restricted stock	(48)	(45)	(353)	(349)
Net income (loss) available to common shareholders, basic	(7,014)	(4,034)	94,932	98,238
Income reallocated to participating restricted stock	(48)	(45)	(353)	(349)
Net income (loss) available to common shareholders, diluted	$ (7,014)	$ (4,034)	$ 94,932	$ 98,238
Earnings Per Share, Basic, Distributed	$ 0.335	$ 0.31	$ 1.34	$ 1.24
Earnings (losses) Per Share, Basic, Undistributed	(0.505)	(0.41)	1.01	1.19
Basic net income (loss) per common share	(0.170)	(0.10)	2.35	2.43
Earnings Per Share, Diluted, Distributed	0.335	0.31	1.34	1.24
Earnings (losses) Per Share, Diluted, Undistributed	(0.505)	(0.41)	1.00	1.19
Diluted net income (loss) per common share	$ (0.170)	$ (0.10)	$ 2.34	$ 2.43