CONSOLIDATED STATEMENTS OF COMPREHENSIVE LOSS (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Statement Of Income And Comprehensive Income [Abstract]
Net income (loss)	$ (350,267)	$ (748,790)	$ (479,588)	$ (750,178)
Postretirement benefits:
Actuarial gain				7
Amortization of prior service costs	92	92	277	277
Income tax expense	(22)	(22)	(66)	(70)
Total comprehensive income (loss)	$ (350,197)	$ (748,720)	$ (479,377)	$ (749,964)