Guarantees and Other Commitments and Contingencies Letters of Credit (Details) $ in Thousands	Dec. 31, 2017 USD ($)
Guarantor Obligations
Letters of Credit Outstanding, Amount	$ 32,574
Collateral Supporting Letters of Credit
Guarantor Obligations
Letters of Credit Outstanding, Amount	$ 3,205

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.

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