Fair Value of Financial Instruments - Narrative (Details) - Level 2 - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Jun. 30, 2018	Sep. 30, 2017
Market Approach Valuation Technique | Junior subordinated notes
Financial Instruments Not Measured at Fair Value
Market interest rate (as a percent)	7.33%	6.37%
Market Approach Valuation Technique | Mortgages | Minimum
Financial Instruments Not Measured at Fair Value
Market interest rate (as a percent)	4.10%	3.78%
Market Approach Valuation Technique | Mortgages | Maximum
Financial Instruments Not Measured at Fair Value
Market interest rate (as a percent)	5.83%	5.02%
Carrying and Fair Value | Junior subordinated notes
Financial Instruments Not Measured at Fair Value
Estimated fair value (lower) higher than carrying value	$ 12,608	$ 15,705
Carrying and Fair Value | Mortgages
Financial Instruments Not Measured at Fair Value
Estimated fair value (lower) higher than carrying value	$ 27,252	$ 11,400