Derivatives Hedges and Financial Instruments (Tables)

12 Months Ended

Dec. 31, 2020

Derivative Instruments And Hedging Activities Disclosure [Abstract]

Assets and Liabilities Measured at Fair Value on Recurring Basis

The following details our assets and liabilities that are measured at fair value on a recurring basis at December 31, 2020 and 2019:

			Fair Value Measurements at December 31, 2020 Using
Description	Total Fair Value at December 31, 2020		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3) (1)		Total Fair Value at December 31, 2019
	(In Thousands)
Assets - Supplies, prepaid items and other:
Natural gas contracts	$	80	$	—	$	80	$	—	$	—
Total	$	80	$	—	$	80	$	—	$	—
Liabilities - Current and noncurrent accrued and    other liabilities:
Natural gas contracts	$	1,285	$	—	$	1,285	$	—	$	—
Embedded derivative	$	1,029	$	—	$	—	$	1,029	$	1,084
Total	$	2,314	$	—	$	1,285	$	1,029	$	1,084

(1) There was no Level 3 transfer activity during 2020, 2019 or 2018.