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, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
NUMERATORS:
Net income	$ 56,812	$ 54,287	$ 102,815	$ 101,856	$ 232,940
Dividends and undistributed earnings allocated to participating securities	14	32	26	61
Net earnings available to common shareholders	$ 56,798	$ 54,255	$ 102,789	$ 101,795
DENOMINATORS:
Weighted average number of common shares outstanding - basic (in shares)	220,310	220,421	220,298	220,324
Effect of potentially dilutive common shares (in shares)	443	486	492	677
Weighted average number of common shares outstanding - diluted (in shares)	220,753	220,907	220,790	221,001
EARNINGS PER COMMON SHARE:
Basic (in usd per share)	$ 0.26	$ 0.25	$ 0.47	$ 0.46
Diluted (in usd per share)	$ 0.26	$ 0.25	$ 0.47	$ 0.46