Commitments and Contingent Liabilities - Commitments to Extend Credit, Participations Sold (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Commitments to extend credit
Commitments
Participations sold to other institutions	$ 60.5	$ 94.5
Standby letters of credit
Commitments
Participations sold to other institutions	$ 17.8	$ 19.0

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