Loans and Asset Quality Information (Details 4) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2013	Dec. 31, 2012
Purchased impaired loans (substantially all of which are covered loans)
Balance, beginning, carrying value	$ 4,825	$ 8,784
Change due to payments received	(99)	(399)
Transfer to foreclosed real estate		(4,149)
Change due to loan charge-off		172
Other		417
Balance, ending, carrying value	4,726	4,825
Contractual Principal Receivable
Purchased impaired loans (substantially all of which are covered loans)
Balance, beginning, contractual principal	8,815	18,316
Change due to payments received	(41)	(355)
Transfer to foreclosed real estate		(7,636)
Change due to loan charge-off		(359)
Other		(1,151)
Balance, ending, contractual principal	8,774	8,815
Fair Value Adjustment Write Down
Purchased impaired loans (substantially all of which are covered loans)
Balance, beginning, FMV	3,990	9,532
Change due to payments received	58	44
Transfer to foreclosed real estate		(3,487)
Change due to loan charge-off		(531)
Other		(1,568)
Balance, ending, FMV	$ 4,048	$ 3,990