Income Taxes (Details) (USD $)
 3 Months Ended 12 Months Ended
Dec. 31, 2014
Sep. 30, 2014
Jun. 30, 2014
Mar. 31, 2014
Dec. 31, 2013
Sep. 30, 2013
Jun. 30, 2013
Mar. 31, 2013
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Components of income taxes                      
Current                 $ 4,830,000 $ 4,020,000 $ 1,926,000
Deferred                 12,704,000 10,091,000 8,571,000
Total income tax expense 4,763,000 4,708,000 4,025,000 4,038,000 3,528,000 3,572,000 3,787,000 3,224,000 17,534,000 14,111,000 10,497,000
Reconciliation of federal and state income taxes at statutory rates to the income taxes included in the statements of operations                      
Income tax at statutory rate (as a percent)                 35.00% 35.00% 35.00%
Tax-exempt interest, net (as a percent)                 (2.60%) (3.50%) (4.50%)
State income taxes, net (as a percent)                 5.70% 4.50% 3.50%
Income on bank owned life insurance (as a percent)                 (1.00%) (0.90%) (1.80%)
Other, net (as a percent)                 (2.20%) (2.20%) (0.30%)
Total (as a percent)                 34.90% 32.90% 31.90%
Deferred tax assets:                      
Allowance for loan losses 18,904,000       19,416,000       18,904,000 19,416,000  
Stock-based compensation 1,472,000       1,319,000       1,472,000 1,319,000  
Loan adjustments 94,000       108,000       94,000 108,000  
Deferred compensation 2,057,000       2,015,000       2,057,000 2,015,000  
Accrued vacation 527,000       545,000       527,000 545,000  
Employee costs 656,000       1,264,000       656,000 1,264,000  
Other 2,498,000       1,780,000       2,498,000 1,780,000  
Total 26,208,000       26,447,000       26,208,000 26,447,000  
Investment securities:                      
Unrealized gains on securities available for sale (3,884,000)       (3,119,000)       (3,884,000) (3,119,000)  
Other (1,997,000)       (2,450,000)       (1,997,000) (2,450,000)  
Basis in premises and equipment (2,012,000)       (2,590,000)       (2,012,000) (2,590,000)  
Mortgage servicing assets (1,549,000)       (2,097,000)       (1,549,000) (2,097,000)  
Basis in core deposit and customer intangible assets (2,669,000)       (3,908,000)       (2,669,000) (3,908,000)  
Deferred loan origination costs (257,000)       (20,000)       (257,000) (20,000)  
Deferred tax liabilities (12,368,000)       (14,184,000)       (12,368,000) (14,184,000)  
Net operating loss carryforward, net of valuation allowance 8,333,000       23,379,000       8,333,000 23,379,000  
Net deferred tax assets 22,173,000       35,642,000       22,173,000 35,642,000  
Operating loss carryforwards                      
Valuation allowance required for other deferred tax assets 0               0    
Indiana and Florida                      
Operating loss carryforwards                      
Net operating loss carryforwards 1,000,000       1,500,000       1,000,000 1,500,000  
Valuation allowance 1,000,000               1,000,000    
Federal                      
Operating loss carryforwards                      
Net operating loss carryforwards         33,000,000         33,000,000  
Illinois                      
Operating loss carryforwards                      
Net operating loss carryforwards $ 114,000,000       $ 171,000,000       $ 114,000,000 $ 171,000,000