Accounting for Certain Loans Acquired in a Purchase - Carrying Amount of Loans Included in Balance Sheet (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Acquired	$ 634,718	$ 690,218
Carrying Amount	593,996	636,182
Allowance	382	229
Carrying Amount Net of Allowance	593,614	635,953
Commercial and industrial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Acquired	86,211	89,487
Agricultural production financing and other loans to farmers
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Acquired	793	1,161
Real estate loans - Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Acquired	14,830	17,962
Real estate loans - Commercial and farm land
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Acquired	305,247	335,049
Real estate loans - Residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Acquired	165,310	176,113
Real estate loans - Home equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Acquired	60,540	67,278
Individuals' loans for household and other personal expenditures
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Acquired	1,699	2,629
Other loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Acquired	88	539
Merger with CFS Bancorp, Inc. (Citizens)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Acquired	581,546	629,184
Carrying Amount	549,167	585,913
Allowance	365
Carrying Amount Net of Allowance	548,802	585,913
Merger with CFS Bancorp, Inc. (Citizens) | Commercial and industrial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Acquired	78,574	81,303
Merger with CFS Bancorp, Inc. (Citizens) | Real estate loans - Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Acquired	14,830	17,962
Merger with CFS Bancorp, Inc. (Citizens) | Real estate loans - Commercial and farm land
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Acquired	285,428	311,631
Merger with CFS Bancorp, Inc. (Citizens) | Real estate loans - Residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Acquired	157,355	166,754
Merger with CFS Bancorp, Inc. (Citizens) | Real estate loans - Home equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Acquired	43,745	49,042
Merger with CFS Bancorp, Inc. (Citizens) | Individuals' loans for household and other personal expenditures
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Acquired	1,526	2,360
Merger with CFS Bancorp, Inc. (Citizens) | Other loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Acquired	88	132
SCB Bank
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Acquired	53,172	61,034
Carrying Amount	44,829	50,269
Allowance	17	229
Carrying Amount Net of Allowance	44,812	50,040
SCB Bank | Commercial and industrial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Acquired	7,637	8,184
SCB Bank | Agricultural production financing and other loans to farmers
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Acquired	793	1,161
SCB Bank | Real estate loans - Commercial and farm land
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Acquired	19,819	23,418
SCB Bank | Real estate loans - Residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Acquired	7,955	9,359
SCB Bank | Real estate loans - Home equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Acquired	16,795	18,236
SCB Bank | Individuals' loans for household and other personal expenditures
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Acquired	173	269
SCB Bank | Other loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Acquired		$ 407