Quarterly report pursuant to Section 13 or 15(d)

Debt - Interest Rate Contracts (Details)

v3.8.0.1
Debt - Interest Rate Contracts (Details) - Cash Flow Hedging - Designated as Hedging Instrument - Interest rate swap contracts - USD ($)
6 Months Ended 12 Months Ended
Mar. 31, 2018
Sep. 30, 2017
Derivative [Line Items]    
Pay fixed swaps - notional amount $ 404,688,000 $ 414,063,000
Net unrealized gain $ 9,912,000 $ 3,959,000
Weighted-average maturity period (years) 2 years 9 months 24 days 3 years 3 months 24 days
Weighted-average received rate (as a percent) 1.88% 1.23%
Weighted-average pay rate (as a percent) 1.35% 1.34%