Commitments and Contingent Liabilities - Schedule of Contract Amounts Represent Credit Risk (Detail) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Credit enhancement under the Federal Home Loan Bank of Chicago Mortgage Partnership Finance Program	$ 7,641	$ 7,644
Letters of Credit
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Contract amounts represent credit risk	3,944	8,564
Commitments to Extend Credit
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Contract amounts represent credit risk	94,340	39,251
Home Equity
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Contract amounts represent credit risk	111,510	111,365
Credit Cards
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Contract amounts represent credit risk	0	23,249
Commercial
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Contract amounts represent credit risk	$ 237,172	$ 144,333