Quarterly Financial Data (Unaudited) (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Quarterly Financial Information Disclosure [Abstract]
Interest income	$ 94,254	$ 95,991	$ 100,990	$ 97,965	$ 97,329	$ 101,379	$ 102,347	$ 103,237	$ 389,200	$ 404,292	$ 445,133
Interest expense	18,147	20,683	22,080	23,612	25,520	26,543	27,540	29,494	84,522	109,097	161,106
Net interest income	76,107	75,308	78,910	74,353	71,809	74,836	74,807	73,743	304,678	295,195	284,027
Provision for credit losses	0	2,000	4,000	4,000	4,000	6,000	10,000	10,000	10,000	30,000	250,229
Net interest income after provision for credit losses	76,107	73,308	74,910	70,353	67,809	68,836	64,807	63,743	294,678	265,195	33,798
Noninterest Income	31,227	46,698	44,741	31,587	32,899	29,112	34,335	29,982	154,253	126,328	136,965
Noninterest expense	89,589	89,408	87,607	88,649	85,875	86,620	91,587	88,308	355,253	352,390	395,045
Income before income taxes	17,745	30,598	32,044	13,291	14,833	11,328	7,555	5,417	93,678	39,133	(224,282)
Income Tax Expense (Benefit)	3,201	0	288,842	0	0	0	0	0	292,043	0	0
Net income	$ 20,946	$ 30,598	$ 320,886	$ 13,291	$ 14,833	$ 11,328	$ 7,555	$ 5,417	$ 385,721	$ 39,133	$ (224,282)
Earnings per share - basic (in dollars per share)	$ 0.34	$ 0.49	$ 5.17	$ 0.21	$ 0.24	$ 0.18	$ 0.12	$ 0.09	$ 6.21	$ 0.63	$ (53.05)
Earnings per share - diluted (in dollars per share)	$ 0.33	$ 0.49	$ 5.13	$ 0.21	$ 0.24	$ 0.18	$ 0.12	$ 0.09	$ 6.14	$ 0.63	$ (53.05)
Weighted Average Number of Shares Outstanding, Basic	62,159,683	62,139,833	62,112,936	62,078,404	61,989,094	61,958,183	61,943,851	61,930,783	62,122,862	61,955,659	14,253,869
Weighted average shares outstanding - diluted (in shares)	62,867,030	62,845,864	62,610,054	62,682,987	62,194,011	62,041,203	62,312,224	62,335,212	62,772,079	62,231,208	14,253,869