Deposits - Additional Information (Detail) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Banking and Thrift [Abstract]
Time deposits, $100,000 and over	$ 119.4	$ 84.9

Amount of time deposit liabilities, including certificates of deposit, in denominations of $100,000 or more.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher SEC
-Name Industry Guide
-Number 3
-Section V
-Paragraph D-E