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		12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
NUMERATORS:
Net income	$ 46,003	$ 47,569	$ 232,940
Dividends and undistributed earnings allocated to participating securities	12	29
Net earnings available to common shareholders	$ 45,991	$ 47,540
DENOMINATORS:
Weighted average number of common shares outstanding - basic (in shares)	220,287	220,227
Effect of potentially dilutive common shares (in shares)	492	825
Weighted average number of common shares outstanding - diluted (in shares)	220,779	221,052
EARNINGS PER COMMON SHARE:
Basic (in usd per share)	$ 0.21	$ 0.22
Diluted (in usd per share)	$ 0.21	$ 0.22