Commitments and Contingent Liabilities - Commitments to Extend Credit, Participations Sold (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Commitments to extend credit
Commitments
Participations sold to other institutions	$ 94.5	$ 72.7
Standby letters of credit
Commitments
Participations sold to other institutions	$ 19.0	$ 18.0

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