Consolidated Quarterly Financial Data (Unaudited) (Summary Of Consolidated Quarterly Financial Data) (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Consolidated Quarterly Financial Data (Unaudited) [Abstract]
Interest income	$ 166,572	$ 171,639	$ 167,794	$ 167,819	$ 165,090	$ 170,586	$ 171,187	$ 169,949	$ 673,824	$ 676,812	$ 712,184
Interest expense	48,258	49,704	50,124	50,927	51,949	52,852	54,161	55,098	199,013	214,060	262,870
Net interest income	118,314	121,935	117,670	116,892	113,141	117,734	117,026	114,851	474,811	462,752	449,314
Provision for credit losses	15,364	7,783	6,026	24,162	15,099	9,308	12,438	12,611	53,335	49,456	47,992
Gains on securities transactions, net	12,034	863	16,492	2,679	6,967	112	3,656	863	32,068	11,598	8,005
Net impairment losses on securities recognized in earnings	(19,143)			(825)			(2,049)	(2,593)	19,968	4,642	6,352
Trading (losses) gains, net	(839)	776	(1,048)	3,382	(2,078)	(2,627)	838	(3,030)	2,271	(6,897)	(10,434)
Other non-interest income	21,720	18,564	18,091	39,551	30,957	19,843	20,031	20,437	15,921	16,015	17,043
Non-interest expense	84,377	85,302	83,080	83,829	80,408	78,947	79,973	78,354	336,588	317,682	306,028
Income before income taxes	32,345	49,053	62,099	53,688	53,480	46,807	47,091	39,563	197,185	186,941	167,545
Income tax expense	7,528	13,696	25,205	17,103	15,322	14,168	14,081	12,200	63,532	55,771	51,484
Net income	$ 24,817	$ 35,357	$ 36,894	$ 36,585	$ 38,158	$ 32,639	$ 33,010	$ 27,363	$ 133,653	$ 131,170	$ 116,061
Earnings per common share, Basic	$ 0.15	$ 0.21	$ 0.22	$ 0.22	$ 0.23	$ 0.19	$ 0.20	$ 0.16	$ 0.79	$ 0.78	$ 0.61
Earnings per common share, Diluted	$ 0.15	$ 0.21	$ 0.22	$ 0.22	$ 0.23	$ 0.19	$ 0.20	$ 0.16	$ 0.79	$ 0.78	$ 0.61
Cash dividends declared per common share	$ 0.17	$ 0.17	$ 0.17	$ 0.17	$ 0.17	$ 0.17	$ 0.17	$ 0.17	$ 0.69	$ 0.69	$ 0.69
Average common shares outstanding, Basic	170,185,439	170,007,399	169,843,354	169,671,128	169,426,058	169,177,275	169,009,302	168,831,733	169,928,460	169,112,901	159,259,476
Average common shares outstanding, Diluted	170,185,880	170,007,983	169,852,912	169,678,846	169,428,992	169,178,469	169,013,634	168,834,400	169,929,590	169,121,584	159,260,229