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

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Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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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 ($)			3 Months Ended		9 Months Ended
Equity and Financing Arrangements (Details) - USD ($)	Oct. 02, 2017	Jan. 13, 2017	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Common Stock [Abstract]
Common stock issued during period			0	0	0	0
Dilutive Shares Calculation [Abstract]
Dilutive securities					$ 0
Medium-Term Notes, 5.26% due 2017
Debt Instrument [Line Items]
Long-term debt, gross		$ 30,000,000
Senior Notes, 3.76% due 2052
Debt Instrument [Line Items]
Long-term debt, gross		$ 40,000,000
Interest rate		3.76%
Term		35 years
Future Debt Issuance, 3.11% due 2027 \| Subsequent Event [Member]
Debt Instrument [Line Items]
Long-term debt, gross	$ 30,000,000
Interest rate	3.11%
Term	10 years