CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Unaudited) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Statement Of Income And Comprehensive Income [Abstract]
Net (loss) income	$ (146,569)	$ 115,185	$ (1,594)	$ 116,604
Postretirement benefits:
Actuarial (loss) gain		(12)	7	(24)
Amortization of prior service costs	93	92	185	184
Income tax expense	(22)	(20)	(48)	(40)
Total comprehensive (loss) income	$ (146,498)	$ 115,245	$ (1,450)	$ 116,724

Amount after tax of increase (decrease) in equity from transactions and other events and circumstances from net income and other comprehensive income, attributable to parent entity. Excludes changes in equity resulting from investments by owners and distributions to owners.

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Amount of tax (expense) benefit for cost (credit) of benefit change attributable to participants' prior service from plan amendment or plan initiation of defined benefit plan, that has not been recognized in net periodic benefit cost (credit).

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