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Commitments - Summary of Financial Instrument Commitments (Details) - USD ($) $ in Thousands | Dec. 31, 2017 | Dec. 31, 2016
--- | --- | ---
Fixed |  |
Financial instrument commitments |  |
Financial instrument commitments | $ 418 | $ 315
Loan commitments | 82,942 | 68,996
Fixed | Borrower |  |
Financial instrument commitments |  |
Financial instrument commitments | 418 | 220
Fixed | Borrower | Financial standby |  |
Financial instrument commitments |  |
Financial instrument commitments | 177 | 137
Fixed | Borrower | Performance standby |  |
Financial instrument commitments |  |
Financial instrument commitments | 241 | 83
Fixed | Nonborrower | Performance standby |  |
Financial instrument commitments |  |
Financial instrument commitments |  | 95
Variable |  |
Financial instrument commitments |  |
Financial instrument commitments | 11,860 | 13,196
Loan commitments | 260,061 | 270,989
Variable | Borrower |  |
Financial instrument commitments |  |
Financial instrument commitments | 11,718 | 12,672
Variable | Borrower | Financial standby |  |
Financial instrument commitments |  |
Financial instrument commitments | 3,770 | 4,047
Variable | Borrower | Commercial standby |  |
Financial instrument commitments |  |
Financial instrument commitments | 354 | 126
Variable | Borrower | Performance standby |  |
Financial instrument commitments |  |
Financial instrument commitments | 7,594 | 8,499
Variable | Nonborrower | Performance standby |  |
Financial instrument commitments |  |
Financial instrument commitments | 142 | 524
Total. |  |
Financial instrument commitments |  |
Financial instrument commitments | 12,278 | 13,511
Loan commitments | 343,003 | 339,985
Total. | Borrower |  |
Financial instrument commitments |  |
Financial instrument commitments | 12,136 | 12,892
Total. | Borrower | Financial standby |  |
Financial instrument commitments |  |
Financial instrument commitments | 3,947 | 4,184
Total. | Borrower | Commercial standby |  |
Financial instrument commitments |  |
Financial instrument commitments | 354 | 126
Total. | Borrower | Performance standby |  |
Financial instrument commitments |  |
Financial instrument commitments | 7,835 | 8,582
Total. | Nonborrower | Performance standby |  |
Financial instrument commitments |  |
Financial instrument commitments | $ 142 | $ 619

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