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Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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Face (par) amount of debt instrument at time of issuance.

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Contractual interest rate for funds borrowed, under the debt agreement.

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Amount of increase (decrease) to net income used for calculating diluted earnings per share (EPS), resulting from the assumed exercise stock options, restrictive stock units (RSUs), convertible preferred stock of an employee stock ownership plan (ESOP), and other dilutive convertible securities.

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Number of new stock issued during the period.

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Equity and Financing Arrangements (Details) - USD ($)			9 Months Ended
Equity and Financing Arrangements (Details) - USD ($)	Sep. 07, 2018	Jul. 16, 2018	Sep. 30, 2018	Sep. 30, 2017
Common Stock [Abstract]
Common stock issued during period			0	0
Dilutive Shares Calculation [Abstract]
Dilutive securities			$ 0
Senior Notes, 4.24% due 2053
Debt Instrument [Line Items]
Face amount		$ 20,000,000
Interest rate		4.24%
Term		35 years
Senior Notes, 4.34% due 2058
Debt Instrument [Line Items]
Face amount		$ 20,000,000
Interest rate		4.34%
Term		40 years
Senior Notes, 4.19% due 2048
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