Commitments and Contingent Liabilities Commitments (Details) - Principal Shareholder of more than 5% [Member] - Oklahoma Historic State Income Tax Credit [Member] $ in Millions	12 Months Ended
Dec. 31, 2016 USD ($)
Purchase Commitment, Excluding Long-term Commitment [Line Items]
Original commitment to purchase tax credits from related party	$ 7.5
Related Party Transaction, Purchases from Related Party	$ 3.8

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

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