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 ($)
$ in Thousands
3 Months Ended 12 Months Ended
Dec. 31, 2017
Sep. 30, 2017
Derivative [Line Items]    
Pay fixed swaps - notional amount $ 409,375 $ 414,063
Net unrealized gain (loss) $ 6,573 $ 3,959
Weighted-average maturity period (years) 3 years 1 month 24 days 3 years 3 months 24 days
Weighted-average received rate (as a percent) 1.56% 1.23%
Weighted-average pay rate (as a percent) 1.34% 1.34%