Borrowings - Short Term Borrowings (Details) - USD ($)	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Short-term borrowings:
Short-Term	$ 0	$ 0
Maximum outstanding at any month end	300,000,000	300,000,000
Secured Borrowing Facility
Short-term borrowings:
Short-Term	$ 0	$ 0
Weighted Average Interest Rate	0.00%	0.00%
Average Balance	$ 52,603,000	$ 81,370,000
Weighted Average Interest Rate	8.91%	6.09%
Commercial Paper \| Secured Borrowing Facility
Short-term borrowings:
Short-Term	$ 0	$ 0

The average effective interest rate during the reporting period.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
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Weighted average interest rate of short-term debt outstanding calculated at point in time.

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For the form of debt having an initial term of less than one year or less than the normal operating cycle, if longer, average borrowings during the period.

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No definition available.

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For the form of debt having an initial term of less than one year or less than the normal operating cycle, if longer, maximum month-end borrowings during the period.

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