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Derivatives, Hedging Activities and Financial Instruments with Off-Balance Sheet Risk - Commitments (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Company's contractual commitments due to letters of credit
Total letters of credit	$ 15,389	$ 12,278
Fixed
Company's contractual commitments due to letters of credit
Total letters of credit	2,931	418
Variable
Company's contractual commitments due to letters of credit
Total letters of credit	12,458	11,860
Borrower
Company's contractual commitments due to letters of credit
Total letters of credit	15,322	12,136
Borrower | Fixed
Company's contractual commitments due to letters of credit
Total letters of credit	2,931	418
Borrower | Variable
Company's contractual commitments due to letters of credit
Total letters of credit	12,391	11,718
Borrower | Financial standby
Company's contractual commitments due to letters of credit
Total letters of credit	7,337	3,947
Borrower | Financial standby | Fixed
Company's contractual commitments due to letters of credit
Total letters of credit	2,017	177
Borrower | Financial standby | Variable
Company's contractual commitments due to letters of credit
Total letters of credit	5,320	3,770
Borrower | Commercial standby
Company's contractual commitments due to letters of credit
Total letters of credit	395	354
Borrower | Commercial standby | Variable
Company's contractual commitments due to letters of credit
Total letters of credit	395	354
Borrower | Performance standby
Company's contractual commitments due to letters of credit
Total letters of credit	7,590	7,835
Borrower | Performance standby | Fixed
Company's contractual commitments due to letters of credit
Total letters of credit	914	241
Borrower | Performance standby | Variable
Company's contractual commitments due to letters of credit
Total letters of credit	6,676	7,594
Nonborrower | Performance standby
Company's contractual commitments due to letters of credit
Total letters of credit	67	142
Nonborrower | Performance standby | Variable
Company's contractual commitments due to letters of credit
Total letters of credit	$ 67	$ 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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