Consolidated Statements of Comprehensive Income - Parenthetical - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019
Reclassification adjustment for loss on derivative instruments included in net income, tax	$ 36	$ (249)
Amortization of postretirement liability losses included in net periodic benefit cost, tax	149	100
Net unrealized gain on available-for-sale investments arising during the period, tax	36	10
Reclassification adjustment for (gain) loss on available-for-sale investments included in net income, tax	$ 0	$ 7

Amount of tax expense (benefit) of reclassification adjustment from accumulated other comprehensive income for unrealized gain (loss) realized upon the sale of available-for-sale securities.

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Amount of tax expense (benefit) of reclassification adjustment from accumulated other comprehensive income of accumulated gain (loss) realized from derivative instruments designated and qualifying as the effective portion of cash flow hedges and an entity's share of an equity investee's deferred hedging gain (loss).

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Amount of tax (expense) benefit for reclassification adjustment from accumulated other comprehensive (income) loss of defined benefit plan.

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Amount of tax expense (benefit) before reclassification adjustments of unrealized holding gain (loss) on available-for-sale securities.

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