Loans and Leases Carrying amount loans covered by loss share agreements (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Loans covered by loss share agreement (carrying amount) [Line Items]
Impaired purchased loans	$ 1,970	$ 3,056
Non impaired purchased loans	7,597	10,291
Total covered loans	9,567	13,347
Commercial Portfolio Segment
Loans covered by loss share agreement (carrying amount) [Line Items]
Impaired purchased loans	1,663	2,553
Non impaired purchased loans	2,834	3,827
Total covered loans	4,497	6,380
Agricultural Portfolio Segment
Loans covered by loss share agreement (carrying amount) [Line Items]
Impaired purchased loans	0	0
Non impaired purchased loans	858	1,659
Total covered loans	858	1,659
Residential Portfolio Segment
Loans covered by loss share agreement (carrying amount) [Line Items]
Impaired purchased loans	0	0
Non impaired purchased loans	3,309	4,158
Total covered loans	3,309	4,158
Consumer Portfolio Segment
Loans covered by loss share agreement (carrying amount) [Line Items]
Impaired purchased loans	307	503
Non impaired purchased loans	596	647
Total covered loans	$ 903	$ 1,150