Acquisition and Divestiture Activity - Schedule of Components of Estimated Fair Value of Intangible Assets (Detail) - 6 months ended Jun. 30, 2015 - USD ($) $ in Millions	Total
Core Deposit Intangible [Member] | Tower Financial Corporation [Member]
Business Acquisition [Line Items]
Estimated Fair Value	$ 4.6
Estimated Useful Lives (Years)	7 years
Core Deposit Intangible [Member] | United Bancorp, Inc. [Member]
Business Acquisition [Line Items]
Estimated Fair Value	$ 5.9
Estimated Useful Lives (Years)	7 years
Core Deposit Intangible [Member] | Founders Financial Corporation [Member]
Business Acquisition [Line Items]
Estimated Fair Value	$ 3.0
Estimated Useful Lives (Years)	7 years
Trust Customer Relationship Intangible [Member] | Tower Financial Corporation [Member]
Business Acquisition [Line Items]
Estimated Fair Value	$ 3.8
Estimated Useful Lives (Years)	12 years
Trust Customer Relationship Intangible [Member] | United Bancorp, Inc. [Member]
Business Acquisition [Line Items]
Estimated Fair Value	$ 4.9
Estimated Useful Lives (Years)	12 years
Trust Customer Relationship Intangible [Member] | Founders Financial Corporation [Member]
Business Acquisition [Line Items]
Estimated Fair Value	$ 2.5
Estimated Useful Lives (Years)	12 years