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Derivatives, Hedging Activities and Financial Instruments with Off-Balance Sheet Risk - Commitments (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Company's contractual commitments due to letters of credit
Total letters of credit	$ 12,273	$ 12,278
Fixed
Company's contractual commitments due to letters of credit
Total letters of credit	533	418
Variable
Company's contractual commitments due to letters of credit
Total letters of credit	11,740	11,860
Borrower
Company's contractual commitments due to letters of credit
Total letters of credit	12,131	12,136
Borrower | Fixed
Company's contractual commitments due to letters of credit
Total letters of credit	533	418
Borrower | Variable
Company's contractual commitments due to letters of credit
Total letters of credit	11,598	11,718
Borrower | Financial standby
Company's contractual commitments due to letters of credit
Total letters of credit	4,444	3,947
Borrower | Financial standby | Fixed
Company's contractual commitments due to letters of credit
Total letters of credit	292	177
Borrower | Financial standby | Variable
Company's contractual commitments due to letters of credit
Total letters of credit	4,152	3,770
Borrower | Commercial standby
Company's contractual commitments due to letters of credit
Total letters of credit	354	354
Borrower | Commercial standby | Variable
Company's contractual commitments due to letters of credit
Total letters of credit	354	354
Borrower | Performance standby
Company's contractual commitments due to letters of credit
Total letters of credit	7,333	7,835
Borrower | Performance standby | Fixed
Company's contractual commitments due to letters of credit
Total letters of credit	241	241
Borrower | Performance standby | Variable
Company's contractual commitments due to letters of credit
Total letters of credit	7,092	7,594
Nonborrower | Performance standby
Company's contractual commitments due to letters of credit
Total letters of credit	142	142
Nonborrower | Performance standby | Variable
Company's contractual commitments due to letters of credit
Total letters of credit	$ 142	$ 142

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The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

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