Cash and Credit Facilities - Narrative (Details) $ in Millions	Sep. 30, 2017 USD ($)
Line of Credit Facility [Line Items]
Line of Credit Facility, Current Borrowing Capacity	$ 9.9
Standby Letters of Credit
Line of Credit Facility [Line Items]
Line of Credit Facility, Current Borrowing Capacity	0.6
Bank revolving line of credit
Line of Credit Facility [Line Items]
Debt Instrument, Unused Borrowing Capacity, Amount	$ 9.3