Property, Plant, and Equipment, net - Schedule of Property, Plant, and Equipment (Detail) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Property, plant and equipment gross	$ 2,695,075	$ 2,742,121
Accumulated depletion and depreciation	(1,312,827)	(1,322,139)
Property, plant, and equipment, net	1,382,248	1,419,982
Land and Improvements [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment gross	225,107	230,300
Mineral Rights Properties [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment gross	664,437	677,238
Machinery and Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment gross	1,315,919	1,338,411
Buildings and Improvements [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment gross	322,468	327,314
Railroad Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment gross	59,917	59,761
Furniture, Fixtures and Other [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment gross	5,148	5,382
Assets Under Construction [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment gross	$ 102,079	$ 103,715