Condensed Consolidated Statements of Comprehensive Income (Parenthetical) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Statement of Comprehensive Income [Abstract]
Net unrealized gain (loss) on cash flow hedges, tax	$ (78)	$ (120)	$ 154	$ 235
Net unrealized gain on investment securities, tax	(447)	758	(1,813)	1,102
Adjustments to pension and postretirement plans, tax				(304)
Amortization of pension and postretirement costs, tax	$ 2,564	$ 3,442	$ 5,368	$ 6,956

Amount of tax expense (benefit), after reclassification adjustments, of appreciation (loss) in value of unsold available-for-sale securities, attributable to parent entity. Excludes amounts related to other than temporary impairment (OTTI) loss.

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Amount, after reclassification, of tax expense (benefit) for gain (loss) from derivative instrument designated and qualifying as cash flow hedge included in assessment of hedge effectiveness, attributable to parent.

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Amount, before reclassification adjustment, of tax (expense) benefit for (increase) decrease in accumulated other comprehensive income for defined benefit plan.

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

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