Securities - Additional Information (Detail) - Jun. 30, 2015 $ in Millions	USD ($) Securities
Investments, Debt and Equity Securities [Abstract]
Number of securities with unrealized losses | Securities	61
Securities pledged to municipalities for deposits in excess of FDIC limits, book value	$ 162.8
Securities pledged to municipalities for deposits in excess of FDIC limits, market value	168.2
Securities with market value sold under agreements to repurchase from various customers	42.2
Wholesale repurchase agreements with combined book value	6.9
Wholesale repurchase agreements with combined market value	7.1
Investment repurchase agreement, amount	$ 6.0
Repurchase agreement, maturity date	Sep. 18, 2016
Repurchase agreement, interest rate	4.36%