CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY - USD ($) $ in Thousands	Total	Series A Preferred Stock	Series B Preferred Stock	Preferred Stock	Common Stock	Treasury Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income (Loss)	Retained Earnings	Retained Earnings Series A Preferred Stock	Retained Earnings Series B Preferred Stock
Beginning Balance (in shares) at Dec. 31, 2015				7,300,000	426,303,244	(4,374,190)
Beginning Balance, shares issued (in shares) at Dec. 31, 2015					430,677,434
Beginning Balance at Dec. 31, 2015	$ 2,096,323			$ 565,000	$ 86,136	$ (41,223)	$ 1,135,860	$ (16,059)	$ 366,609
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	65,915								65,915
Other comprehensive income (loss), net of tax	(13,210)							(13,210)
Total comprehensive income	52,705
Cash dividends:
Cash dividends, preferred stock		$ (2,875)	$ (2,264)							$ (2,875)	$ (2,264)
Dividend equivalent units related to employee stock-based compensation plans	$ 0						399		(399)
Issuance of common shares (in shares)	2,740,979				2,740,979
Issuance of common shares	$ 2,707				$ 548		2,159
Tax benefit related to employee stock-based compensation	(2,132)						(2,132)
Stock-based compensation expense	6,216						6,216
Shares repurchased related to employee stock-based compensation plans (in shares)					(1,128,709)	(1,128,709)
Shares repurchased related to employee stock-based compensation plans	(6,755)					$ (6,755)
Ending Balance (in shares) at Mar. 31, 2016				7,300,000	427,915,514	(5,502,899)
Ending Balance, shares issued (in shares) at Mar. 31, 2016					433,418,413
Ending Balance at Mar. 31, 2016	2,143,925			$ 565,000	$ 86,684	$ (47,978)	1,142,502	(29,269)	426,986
Beginning Balance (in shares) at Dec. 31, 2016				7,300,000	428,903,559	(7,728,920)
Beginning Balance, shares issued (in shares) at Dec. 31, 2016					436,632,479
Beginning Balance at Dec. 31, 2016	2,347,058			$ 565,000	$ 87,327	$ (67,484)	1,175,564	(8,671)	595,322
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	94,943								94,943
Other comprehensive income (loss), net of tax	1,980							1,980
Total comprehensive income	96,923
Cumulative effect of the new stock compensation standard	165						594		(429)
Cash dividends:
Cash dividends, preferred stock		$ (2,875)	$ (2,700)							$ (2,875)	$ (2,700)
Dividend equivalent units related to employee stock-based compensation plans	$ 0						96		(96)
Issuance of common shares (in shares)	3,738,717				3,738,717
Issuance of common shares	$ 6,535				$ 748		5,787
Stock-based compensation expense	9,425						9,425
Shares repurchased related to employee stock-based compensation plans (in shares)					(1,603,487)	(1,603,487)
Shares repurchased related to employee stock-based compensation plans	(19,175)					$ (19,175)
Ending Balance (in shares) at Mar. 31, 2017				7,300,000	431,038,789	(9,332,407)
Ending Balance, shares issued (in shares) at Mar. 31, 2017					440,371,196
Ending Balance at Mar. 31, 2017	$ 2,435,356			$ 565,000	$ 88,075	$ (86,659)	$ 1,191,466	$ (6,691)	$ 684,165