Investment Securities (Details 5) (USD $)	12 Months Ended			3 Months Ended	12 Months Ended							3 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2010 Trust preferred debt securities item	Dec. 31, 2010 Trust preferred debt securities	Dec. 31, 2010 PreTSL IX B-3	Dec. 31, 2010 PreTSL X B-1	Dec. 31, 2010 PreTSL X B-3	Dec. 31, 2010 PreTSL XI B-1	Dec. 31, 2010 PreTSL XIII B-2	Dec. 31, 2010 PreTSL XIV	Dec. 31, 2010 Seven pooled trust preferred securities	Mar. 31, 2011 MMCaps I A
Investment Securities
Carrying value of investment securities pledged to secure public funds deposits and for other purposes required and permitted by law	$ 203,900,000	$ 128,700,000
Carrying amount of the securities pledged to secure repurchase agreements	109,500,000	87,100,000
Roll forward of recognized charges to earnings on certain trust preferred debt securities
Balance at beginning of period					4,922,000
Net fair market value losses recognized in earnings		115,000	130,000		6,640,000	1,284,000	1,550,000	431,000	1,742,000	607,000	1,026,000
Balance at end of period				11,562,000	11,562,000
Additional disclosures
Impairment charge recognized in earnings		115,000	6,770,000		6,600,000
Number of pooled trust preferred securities elected to be sold				7
Total number of pooled trust preferred securities				8
Incremental loss on sale of securities	$ (189,000)	$ (323,000)	$ (292,000)									$ 1,300,000	$ 194,000