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Income Taxes - Significant Components of Temporary Differences (Details) - USD ($) $ in Thousands | Dec. 31, 2017 | Dec. 31, 2016
--- | --- | ---
Deferred Tax Assets: |  |
Allowance for loan losses | $ 12,440 | $ 19,446
Purchase accounting adjustments | 0 | 365
Other employee benefits | 3,095 | 3,983
Low income housing partnerships | 3,213 | 4,845
Net adjustment to funded status of pension | 6,481 | 10,018
Impairment of securities | 300 | 1,318
State net operating loss carryforwards | 3,598 | 3,114
Other | 2,355 | 4,984
Gross Deferred Tax Assets | 31,482 | 48,073
Less: Valuation allowance | (3,598) | (3,114)
Total Deferred Tax Assets | 27,884 | 44,959
Deferred Tax Liabilities: |  |
Net unrealized holding gains on securities available-for-sale | (638) | (2,557)
Prepaid pension | (1,749) | (2,770)
Deferred loan income | (2,937) | (3,815)
Purchase accounting adjustments | (100) | 0
Depreciation on premises and equipment | (480) | (1,239)
Other | (1,401) | (1,766)
Total Deferred Tax liabilities | (7,305) | (12,147)
Net Deferred Tax Asset | $ 20,579 | $ 32,812

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