Accounting for Certain Loans Acquired in a Purchase - Carrying Amount of Loans Included in Balance Sheet (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Acquired	$ 660,617	$ 690,218
Carrying Amount	616,739	636,182
Allowance	443	229
Carrying Amount Net of Allowance	616,296	635,953
Commercial and industrial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Acquired	85,319	89,487
Agricultural production financing and other loans to farmers
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Acquired	941	1,161
Real estate loans - Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Acquired	15,610	17,962
Real estate loans - Commercial and farm land
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Acquired	321,415	335,049
Real estate loans - Residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Acquired	170,951	176,113
Real estate loans - Home equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Acquired	64,122	67,278
Individuals' loans for household and other personal expenditures
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Acquired	2,169	2,629
Other loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Acquired	90	539
Merger with CFS Bancorp, Inc. (Citizens)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Acquired	605,105	629,184
Carrying Amount	570,092	585,913
Allowance	426
Carrying Amount Net of Allowance	569,666	585,913
Merger with CFS Bancorp, Inc. (Citizens) | Commercial and industrial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Acquired	77,480	81,303
Merger with CFS Bancorp, Inc. (Citizens) | Real estate loans - Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Acquired	15,610	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	301,268	311,631
Merger with CFS Bancorp, Inc. (Citizens) | Real estate loans - Residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Acquired	162,265	166,754
Merger with CFS Bancorp, Inc. (Citizens) | Real estate loans - Home equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Acquired	46,428	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	1,964	2,360
Merger with CFS Bancorp, Inc. (Citizens) | Other loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Acquired	90	132
SCB Bank
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Acquired	55,512	61,034
Carrying Amount	46,647	50,269
Allowance	17	229
Carrying Amount Net of Allowance	46,630	50,040
SCB Bank | Commercial and industrial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Acquired	7,839	8,184
SCB Bank | Agricultural production financing and other loans to farmers
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Acquired	941	1,161
SCB Bank | Real estate loans - Commercial and farm land
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Acquired	20,147	23,418
SCB Bank | Real estate loans - Residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Acquired	8,686	9,359
SCB Bank | Real estate loans - Home equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Acquired	17,694	18,236
SCB Bank | Individuals' loans for household and other personal expenditures
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Acquired	205	269
SCB Bank | Other loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Acquired		$ 407