Accounting for Certain Loans Acquired in a Purchase - Carrying Amount of Loans Included in Balance Sheet (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Acquired	$ 593,070	$ 690,218
Carrying Amount	560,808	636,182
Allowance	459	229
Carrying Amount Net of Allowance	560,349	635,953
Commercial and industrial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Acquired	83,592	89,487
Agricultural production financing and other loans to farmers
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Acquired	959	1,161
Real estate loans - Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Acquired	11,099	17,962
Real estate loans - Commercial and farm land
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Acquired	280,723	335,049
Real estate loans - Residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Acquired	158,171	176,113
Real estate loans - Home equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Acquired	57,245	67,278
Individuals' loans for household and other personal expenditures
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Acquired	1,194	2,629
Other loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Acquired	87	539
Merger with CFS Bancorp, Inc. (Citizens)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Acquired	544,985	629,184
Carrying Amount	519,516	585,913
Allowance	398
Carrying Amount Net of Allowance	519,118	585,913
Merger with CFS Bancorp, Inc. (Citizens) | Commercial and industrial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Acquired	77,186	81,303
Merger with CFS Bancorp, Inc. (Citizens) | Real estate loans - Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Acquired	11,099	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	264,241	311,631
Merger with CFS Bancorp, Inc. (Citizens) | Real estate loans - Residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Acquired	150,454	166,754
Merger with CFS Bancorp, Inc. (Citizens) | Real estate loans - Home equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Acquired	40,864	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	1,054	2,360
Merger with CFS Bancorp, Inc. (Citizens) | Other loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Acquired	87	132
SCB Bank
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Acquired	48,085	61,034
Carrying Amount	41,292	50,269
Allowance	61	229
Carrying Amount Net of Allowance	41,231	50,040
SCB Bank | Commercial and industrial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Acquired	6,406	8,184
SCB Bank | Agricultural production financing and other loans to farmers
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Acquired	959	1,161
SCB Bank | Real estate loans - Commercial and farm land
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Acquired	16,482	23,418
SCB Bank | Real estate loans - Residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Acquired	7,717	9,359
SCB Bank | Real estate loans - Home equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Acquired	16,381	18,236
SCB Bank | Individuals' loans for household and other personal expenditures
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Acquired	140	269
SCB Bank | Other loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Acquired		$ 407