Deposits - Narrative (Details) - USD ($) $ in Millions	Mar. 31, 2018	Sep. 30, 2017
Banking and Thrift [Abstract]
Aggregate amount of certificates of deposit exceeding threshold amount	$ 656.8	$ 608.5

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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Industry Guide
-Number 3
-Section V
-Paragraph D-E