Subsequent Event - Additional Information (Detail) - Alliance [Member] $ / shares in Units, $ in Millions			9 Months Ended
	Oct. 09, 2015 USD ($) $ / shares	Mar. 02, 2015 USD ($) shares	Sep. 30, 2015 Branch	Jun. 30, 2015 USD ($)
Subsequent Event [Line Items]
Deposits				$ 340.0
Assets				$ 415.0
Payments to Acquire Businesses		$ 26.6
Number of Shares Issued | shares		2,459,223
Common stock outstanding percentage		9.00%
Date of Acquisition Agreement			Mar. 02, 2015
Effective Date of Acquisition			Oct. 09, 2015
Number of branch locations | Branch			8
Subsequent Event [Member]
Subsequent Event [Line Items]
Transaction value, cash and stock	$ 97.9
Closing share price | $ / shares	$ 29.01