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	180,085									180,085
Other comprehensive income (loss), net of tax	(11,754)								(11,754)
Total comprehensive income	168,331
Cash dividends:
Cash dividends, preferred stock		$ (8,625)	$ (7,073)								$ (8,625)	$ (7,073)
Dividend equivalent units related to employee stock-based compensation plans	$ 0							402		(402)
Issuance of common shares (in shares)	3,727,574					3,727,574
Issuance of common shares	$ 6,238					$ 745		5,493
Tax benefit related to employee stock-based compensation	(2,457)							(2,457)
Stock-based compensation expense	$ 17,950							17,950
Shares repurchased related to employee stock-based compensation plans (in shares)	1,763,092					1,763,092	1,763,092
Shares repurchased related to employee stock-based compensation plans	$ (11,191)						$ (11,191)
Ending Balance (in shares) at Sep. 30, 2016				7,300,000		428,267,726	(6,137,282)
Ending Balance, shares issued (in shares) at Sep. 30, 2016						434,405,008
Ending Balance at Sep. 30, 2016	2,259,496			$ 565,000		$ 86,881	$ (52,414)	1,157,248	(27,813)	530,594
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	241,931									241,931
Other comprehensive income (loss), net of tax	4,254								4,254
Total comprehensive income	246,185
Cumulative effect of the new stock compensation standard	165							429		(264)
Cash dividends:
Cash dividends, preferred stock		(3,961)	$ (8,616)								$ (3,961)	$ (8,616)
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)	5,652,886					5,652,886
Issuance of common shares	$ 16,467					$ 1,131		15,336
Stock-based compensation expense	$ 21,773							21,773
Shares repurchased related to employee stock-based compensation plans (in shares)	2,666,781					2,666,781	2,666,781
Shares repurchased related to employee stock-based compensation plans	$ (32,231)						$ (32,231)
Ending Balance (in shares) at Sep. 30, 2017				4,000,000		431,889,664	(10,395,701)
Ending Balance, shares issued (in shares) at Sep. 30, 2017						442,285,365
Ending Balance at Sep. 30, 2017	$ 2,421,840			$ 400,000		$ 88,458	$ (99,715)	$ 1,213,198	$ (4,417)	$ 824,316