Long-Term Debt - Letter of Credit Facilities (Details) - USD ($)	Dec. 31, 2018	Sep. 30, 2018	Feb. 21, 2014
Other Letters of Credit Arrangements
Line of Credit Facility [Line Items]
Letters of credit outstanding	$ 18,000,000	$ 19,000,000
Standby Letters of Credit
Line of Credit Facility [Line Items]
Maximum limit on issuance, letters of credit			$ 25,000,000
Letters of credit outstanding	$ 1,000,000	$ 1,000,000