Consolidated Statements of Changes in Shareholders' Equity (USD $) In Thousands, unless otherwise specified	Total	Preferred Stock	Common stock	Warrant	Capital Surplus	Accumulated Other Comprehensive Income (Loss)	Retained Earnings	Treasury Stock
Beginning Balance at Dec. 31, 2011	$ 1,565,953	$ 0	$ 127,937	$ 0	$ 479,882	$ (23,887)	$ 1,131,203	$ (149,182)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	134,106	0	0	0	0	0	134,106	0
Other comprehensive income	7,682	0	0	0	0	7,682	0	0
Comprehensive income	141,788	0	0	0	0	7,682	134,106	0
Cash dividends - common stock	(69,459)	0	0	0	0	0	(69,459)	0
Nonvested (restricted) shares granted	49		0	0	(14,582)	0		14,631
Restricted stock activity	(2,389)	0	0	0	1,219	0	0	(3,608)
Deferred compensation trust	0	0	0	0	200	0	0	(200)
Issuance of a Common Stock warrant to the U.S. Treasury for Citizens TARP warrant	0
Share-based compensation	9,260	0	0	0	9,260	0	0	0
Ending Balance at Dec. 31, 2012	1,645,202	0	127,937	0	475,979	(16,205)	1,195,850	(138,359)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	183,684	0	0	0	0	0	183,684	0
Other comprehensive income	(50,671)	0	0	0	0	(50,671)	0	0
Comprehensive income	133,013	0	0	0	0	(50,671)	183,684	0
Cash dividends - Preferred Stock	(5,337)	0	0	0	0	0	(5,337)	0
Cash dividends - common stock	(96,222)	0	0	0	0	0	(96,222)	0
Nonvested (restricted) shares granted	(6,813)			0	(19,790)			12,977
Common stock issued in connection with Citizens acquisition	925,272				925,272
Restricted stock activity	(2,708)	0	0	0	1,261	0	0	(3,969)
Deferred compensation trust	0	0	0	0	434	0	0	(434)
Issuance Non-Cumulative Perpetual Preferred Stock, Series A	96,550	100,000			(3,450)
Issuance of a Common Stock warrant to the U.S. Treasury for Citizens TARP warrant	3,000			3,000
Share-based compensation	10,937	0	0	0	10,937	0	0	0
Ending Balance at Dec. 31, 2013	2,702,894	100,000	127,937	3,000	1,390,643	(66,876)	1,277,975	(129,785)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	237,951	0	0	0	0	0		0
Other comprehensive income	(5,016)	0	0	0	0	(5,016)	0	0
Comprehensive income	232,935	0	0	0	0	(5,016)	237,951	0
Cash dividends - Preferred Stock	(5,876)	0	0	0	0	0	(5,876)	0
Cash dividends - common stock	(105,333)	0	0	0	0	0	(105,333)	0
Nonvested (restricted) shares granted	99			0	(13,469)		0	13,568
Restricted stock activity	(4,360)	0	0	0	1,219	0	0	(5,579)
Deferred compensation trust	0	0	0	0	775	0	0	(775)
Issuance of a Common Stock warrant to the U.S. Treasury for Citizens TARP warrant	0
Share-based compensation	13,922	0	0	0	13,922	0	0	0
Ending Balance at Dec. 31, 2014	$ 2,834,281	$ 100,000	$ 127,937	$ 3,000	$ 1,393,090	$ (71,892)	$ 1,404,717	$ (122,571)