Consolidated Statements of Changes in Shareholders' Equity (USD $)	Preferred Stock [Member]	Common Stock [Member]	Capital Surplus [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Total
Balance at Dec. 31, 2008	$ 205,126,000	$ 11,944,000	$ 139,471,000	$ 836,642,000	$ (14,717,000)	$ 1,178,466,000
Balance (in shares) at Dec. 31, 2008		57,324,737				57,324,737
Comprehensive income:
Net income per consolidated statements of income	0	0	0	93,047,000	0	93,047,000
Net change in fair value of securities available for sale	0	0	0	0	13,691,000	13,691,000
Net change in prior service cost	0	0	0	0	(1,164,000)	(1,164,000)
Net (increase) decrease in loss	0	0	0	0	566,000	566,000
Comprehensive income						106,140,000
Common stock offering (in shares)		6,216,216
Common stock offering		1,295,000	108,001,000	0	0	109,296,000
Repurchase of preferred stock and warrant	(205,126,000)	0	(10,000,000)	(9,874,000)	0	(225,000,000)
Cash dividends paid on common stock	0	0	0	(53,295,000)	0	(53,295,000)
Cash dividends paid on preferred stock	0	0	0	(11,288,000)	0	(11,288,000)
Common stock issued, long-term incentive plan (in shares)		132,886
Common stock issued, long-term incentive plan		28,000	2,835,000	(1,679,000)	0	1,184,000
Compensation expense, long-term incentive plan	0	0	4,557,000	0	0	4,557,000
Balance at Dec. 31, 2009	0	13,267,000	244,864,000	853,553,000	(1,624,000)	1,110,060,000
Balance (in shares) at Dec. 31, 2009	0	63,673,839				63,673,839
Comprehensive income:
Net income per consolidated statements of income	0	0	0	100,636,000	0	100,636,000
Net change in fair value of securities available for sale	0	0	0	0	(10,967,000)	(10,967,000)
Net change in prior service cost	0	0	0	0	76,000	76,000
Net (increase) decrease in loss	0	0	0	0	1,089,000	1,089,000
Comprehensive income						90,834,000
Cash dividends paid on common stock	0	0	0	(59,302,000)	0	(59,302,000)
Common stock issued, long-term incentive plan (in shares)	0	243,752
Common stock issued, long-term incentive plan	0	51,000	7,047,000	(3,970,000)	0	3,128,000
Compensation expense, long-term incentive plan	0	0	4,824,000	0	0	4,824,000
Other	0	0	(60,000)	0	0	(60,000)
Balance at Dec. 31, 2010		13,318,000	256,675,000	890,917,000	(11,426,000)	1,149,484,000
Balance (in shares) at Dec. 31, 2010		63,917,591				63,917,591
Comprehensive income:
Net income per consolidated statements of income	0	0	0	106,841,000	0	106,841,000
Net change in fair value of securities available for sale	0	0	0	0	24,426,000	24,426,000
Net change in prior service cost	0	0	0	0	(591,000)	(591,000)
Net (increase) decrease in loss	0	0	0	0	(9,288,000)	(9,288,000)
Comprehensive income						121,388,000
Cash dividends paid on common stock	0	0	0	(59,485,000)	0	(59,485,000)
Common stock issued, long-term incentive plan (in shares)		224,907
Common stock issued, long-term incentive plan	0	46,000	5,560,000	(5,747,000)	0	(141,000)
Compensation expense, long-term incentive plan	0	0	3,791,000	0	0	3,791,000
Balance at Dec. 31, 2011	$ 0	$ 13,364,000	$ 266,026,000	$ 932,526,000	$ 3,121,000	$ 1,215,037,000
Balance (in shares) at Dec. 31, 2011		64,142,498				64,142,498