Other Comprehensive Income (Loss) - Accumulated Balances for Each Component of Other Comprehensive Income (Loss), Net of Tax (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Accumulated balances for component of other comprehensive income, net of tax
Unrealized gains on securities	$ 14,972	$ 42,246
Non-credit related portion of previously recorded other-than-temporary impairment on securities	0	(11,319)
Unrealized gains (losses) on derivative instruments	10,346	(638)
Unrecognized losses on defined benefit pension and post-retirement benefit plans obligations	(5,179)	(5,221)
Total accumulated other comprehensive income	$ 20,139	$ 25,068

Amount, after tax, of accumulated unrealized gain (loss) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount, after tax, of accumulated other comprehensive (income) loss for defined benefit plan, that has not been recognized in net periodic benefit cost (credit).

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Accumulated change in equity from transactions and other events and circumstances from non-owner sources, net of tax effect, at period end. Excludes Net Income (Loss), and accumulated changes in equity from transactions resulting from investments by owners and distributions to owners. Includes foreign currency translation items, certain pension adjustments, unrealized gains and losses on certain investments in debt and equity securities, other than temporary impairment (OTTI) losses related to factors other than credit losses on available-for-sale and held-to-maturity debt securities that an entity does not intend to sell and it is not more likely than not that the entity will be required to sell before recovery of the amortized cost basis, as well as changes in the fair value of derivatives related to the effective portion of a designated cash flow hedge.

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Total of accumulated other comprehensive loss related to that portion of other than temporary impairment (OTTI) due to factors other than credit losses on debt securities categorized either as available-for-sale or held-to-maturity that an entity does not intend to sell and which it is not more likely than not that the entity will be required to sell before recovery of the amortized cost basis of the debt security. The amount represented by this item is net of tax, as applicable.

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Amount, after tax, of accumulated gain (loss) on derivative instrument designated and qualifying as cash flow hedge included in assessment of hedge effectiveness.

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