Earnings Per Common Share (Computation Of Basic And Diluted Earnings (Loss) Per Common Share) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
NUMERATORS:
Net income	$ 54,287	$ 54,784	$ 101,856	$ 101,913	$ 222,539
Dividends and undistributed earnings allocated to participating securities	32	93	61	177
Net earnings available to common shareholders	$ 54,255	$ 54,691	$ 101,795	$ 101,736
DENOMINATORS:
Weighted average number of common shares outstanding - basic (in shares)	220,421	220,463	220,324	220,406
Effect of potentially dilutive common shares (in shares)	486	687	677	682
Weighted average number of common shares outstanding - diluted (in shares)	220,907	221,150	221,001	221,088
EARNINGS PER COMMON SHARE:
Basic (in usd per share)	$ 0.25	$ 0.25	$ 0.46	$ 0.46
Diluted (in usd per share)	$ 0.25	$ 0.25	$ 0.46	$ 0.46