Equity and Financing Arrangements (Details) - USD ($)		6 Months Ended
	Jul. 16, 2018	Jun. 30, 2018	Jun. 30, 2017
Common Stock [Abstract]
Common stock issued during period		0	0
Dilutive Shares Calculation [Abstract]
Dilutive securities		$ 0
Future Debt Issuance, 4.24% due 2053 | Subsequent Event [Member]
Debt Instrument [Line Items]
Face amount	$ 20,000,000
Interest rate	4.24%
Term	35 years
Future Debt Issuance, 4.34% due 2058 | Subsequent Event [Member]
Debt Instrument [Line Items]
Face amount	$ 20,000,000
Interest rate	4.34%
Term	40 years
Future Debt Issuance, 4.19% due 2048 | Subsequent Event [Member]
Debt Instrument [Line Items]
Face amount	$ 60,000,000
Interest rate	4.19%
Term	30 years
Senior Notes, 5.59% due 2018
Debt Instrument [Line Items]
Long-term debt, gross		$ 20,000,000