Income Taxes - Tax Effects on Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Gross deferred tax assets:
Net operating loss carry forward and state tax credits	$ 32,173	$ 11,089
Pension and post-retirement benefit costs	13,976	13,303
Alternative minimum tax credit carry forward	7,895	15,971
Property, plant and equipment	7,179	5,474
Accrued expenses	15,336	27,025
Inventories	6,507	774
Third-party products liability	236	231
Stock-based compensation expense	2,390	8,199
Note payable	109	3,724
Interest expense limitation	22,324	0
Lease obligation liability	29,604	0
Other	5,191	8,116
Total deferred tax assets	142,920	93,906
Gross deferred tax liabilities:
Land and mineral property basis difference	(124,182)	(165,002)
Fixed assets and depreciation	(44,314)	(55,596)
Intangibles	(12,541)	(10,346)
Other	(468)	(201)
Total deferred tax liabilities	(181,505)	(231,145)
Net deferred tax liabilities	$ (38,585)	$ (137,239)