Derivatives - Narrative (Details) - Interest Rate Swap - Cash Flow Hedging	3 Months Ended		9 Months Ended
	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2018 USD ($) interest_rate_swap	Mar. 31, 2017 USD ($) interest_rate_swap
Derivative Instruments, Gain (Loss) [Line Items]
Number of new swaps entered into to manage interest rate exposure | interest_rate_swap					3	4
Combined notional amount					$ 300,000,000	$ 300,000,000
Tax benefit related to interest-rate swap unrealized gains and losses	$ 900,000	$ 300,000	$ 2,500,000	$ 300,000
Interest Rate Cash Flow Hedge Gain to be Reclassified During Next 12 Months, Net	$ 1,700,000		$ 1,700,000