Consolidated Statements of Changes in Equity - USD ($) $ in Thousands	Total	Preferred Stock [Member] Series C Preferred Stock [Member]	Common Stock [Member]	Additional Paid-In Capital [Member]	Treasury Stock [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Retained Earnings [Member]
Balance at Dec. 31, 2014	$ 3,041,270	$ 125,980	$ 139,950	$ 2,960,825	$ (187,774)	$ (12,605)	$ 14,894
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	53,963						53,963
Other comprehensive income, net of income taxes	8,954					8,954
Cash dividends declared on common stock	(13,434)						(13,434)
Cash dividends paid on Series C Preferred Stock	(2,559)						(2,559)
Repurchases of common stock	(59,113)			14,515	(73,628)
Restricted share unit activity	(4,418)		274	(4,325)			(367)
Stock options exercised	1,692		105	1,587
Share-based compensation net tax benefit (deficiency)	1,046			1,046
Share-based compensation expense	3,234			3,234
Balance at Mar. 31, 2015	3,030,635	125,980	140,329	2,976,882	(261,402)	(3,651)	52,497
Balance at Dec. 31, 2015	3,000,196	125,980	140,592	2,989,981	(401,511)	(29,819)	174,973
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	52,531						52,531
Other comprehensive income, net of income taxes	29,079					29,079
Cash dividends declared on common stock	(15,069)						(15,069)
Cash dividends paid on Series C Preferred Stock	(2,559)						(2,559)
Repurchases of common stock	(110,985)				(110,985)
Restricted share unit activity	(2,818)		175	(2,993)
Stock options exercised	456		27	429
Share-based compensation net tax benefit (deficiency)	(900)			(900)
Share-based compensation expense	3,337			3,337
Balance at Mar. 31, 2016	$ 2,953,268	$ 125,980	$ 140,794	$ 2,989,854	$ (512,496)	$ (740)	$ 209,876