Earnings Per Share (Computation of Basic and Diluted Earnings Per Share) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		3 Months Ended
		Mar. 31, 2021	Mar. 31, 2020
Earnings Per Share [Abstract]
Net income		$ 173,015	$ 86,589
Preferred dividends		8,289	4,844
Net income available to common shareholders		$ 164,726	$ 81,745
Average shares used in basic computation		107,746	106,929
Dilutive effect of stock options and units	[1]	10,129	8,000
Average shares used in diluted computation		117,875	114,929
Basic		$ 1.53	$ 0.76
Diluted		$ 1.40	$ 0.71

[1] Diluted earnings per share is computed on the basis of the weighted-average number of shares of common stock plus the effect of dilutive potential common shares outstanding during the period using the treasury stock method.