Earnings per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Basic earnings per share:
Net income	$ 157,977	$ 130,811	$ 461,049	$ 294,663
Weighted average common shares outstanding - basic (in shares)	335,938	338,598	338,045	340,408
Basic earnings per share (in dollars per share)	$ 0.47	$ 0.39	$ 1.36	$ 0.87
Diluted earnings per share:
Net income	$ 157,977	$ 130,811	$ 461,049	$ 294,663
Diluted income available to common shareholders	$ 161,689	$ 134,972	$ 472,184	$ 307,956
Weighted average common shares outstanding - basic (in shares)	335,938	338,598	338,045	340,408
Effect of dilutive securities:
Weighted average common shares outstanding - diluted (in shares)	353,557	357,195	355,481	360,389
Diluted earnings per share (in dollars per share)	$ 0.46	$ 0.38	$ 1.33	$ 0.85
Federal statutory income tax rate (in hundredths)	21.00%	21.00%	21.00%	21.00%
9% Convertible Junior Subordinated Debentures
Diluted earnings per share:
Dilutive securities	$ 3,712	$ 4,161	$ 11,135	$ 13,293
Effect of dilutive securities:
Dilutive securities (in shares)	15,785	17,220	15,785	18,489
Stated interest rate	9.00%		9.00%
Unvested RSUs
Effect of dilutive securities:
Unvested RSUs (in shares)	1,834	1,377	1,651	1,492