CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY - USD ($) $ in Thousands	Total	Series A Preferred Stock	Series B Preferred Stock	Preferred Stock	Preferred Stock Series A 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	123,120									123,120
Other comprehensive income (loss), net of tax	(17,794)								(17,794)
Total comprehensive income	105,326
Cash dividends:
Cash dividends, preferred stock		$ (5,750)	$ (4,632)								$ (5,750)	$ (4,632)
Dividend equivalent units related to employee stock-based compensation plans	$ 0							400		(400)
Issuance of common shares (in shares)	3,166,474					3,166,474
Issuance of common shares	$ 3,857					$ 633		3,224
Tax benefit related to employee stock-based compensation	(2,249)							(2,249)
Stock-based compensation expense	12,548							12,548
Shares repurchased related to employee stock-based compensation plans (in shares)						(1,391,927)	(1,391,927)
Shares repurchased related to employee stock-based compensation plans	(8,512)						$ (8,512)
Ending Balance (in shares) at Jun. 30, 2016				7,300,000		428,077,791	(5,766,117)
Ending Balance, shares issued (in shares) at Jun. 30, 2016						433,843,908
Ending Balance at Jun. 30, 2016	2,196,911			$ 565,000		$ 86,769	$ (49,735)	1,149,783	(33,853)	478,947
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	165,560									165,560
Other comprehensive income (loss), net of tax	819								819
Total comprehensive income	166,379
Cumulative effect of the new stock compensation standard	165							429		(264)
Cash dividends:
Cash dividends, preferred stock		(3,961)	$ (5,588)								$ (3,961)	$ (5,588)
Redemption of Series A Preferred Stock (in shares)					(3,300,000)
Redemption of Series A Preferred Stock		$ (165,000)			$ (165,000)
Dividend equivalent units related to employee stock-based compensation plans	$ 0							96		(96)
Issuance of common shares (in shares)	5,229,774					5,229,774
Issuance of common shares	$ 14,494					$ 1,046		13,448
Stock-based compensation expense	15,500							15,500
Shares repurchased related to employee stock-based compensation plans (in shares)						(2,584,964)	(2,584,964)
Shares repurchased related to employee stock-based compensation plans	(31,337)						$ (31,337)
Ending Balance (in shares) at Jun. 30, 2017				4,000,000		431,548,369	(10,313,884)
Ending Balance, shares issued (in shares) at Jun. 30, 2017						441,862,253
Ending Balance at Jun. 30, 2017	$ 2,337,710			$ 400,000		$ 88,373	$ (98,821)	$ 1,205,037	$ (7,852)	$ 750,973