Income Taxes Schedule of Reconciliation of Income Tax Expense (Benefit) (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Amount
Statutory U.S. federal income tax rate									$ 39,399	$ 59,429	$ 22,755
State income taxes, net of federal tax benefit									3,240	1,264	997
Foreign income taxes									1,436	0	0
Excess tax depletion									(20,873)	(24,216)	(21,856)
Effect of domestic production activities									0	(6,493)	1,621
Effect of change in U.S. tax law									2,777	58,558	0
IRS and state tax examination settlements									0	0	13,958
Effect of valuation allowance									(1,379)	1,379	0
Research and development credit									(980)	0	0
Non-controlling interest									(5,420)	0	0
State rate change and prior period adjustments									(8,223)	0	0
Other									(1,149)	(2,693)	(2,910)
Income Tax Expense / Effective Rate	$ 301	$ (690)	$ 3,032	$ 6,185	$ 64,441	$ 3,770	$ 9,611	$ 9,406	$ 8,828	$ 87,228	$ 14,565
Percent
Statutory U.S. federal income tax rate (as a percent)									21.00%	35.00%	35.00%
State income taxes, net of federal tax benefit (as a percent)									1.70%	0.70%	1.50%
Foreign income taxes (as a percent)									0.80%	0.00%	0.00%
Excess tax depletion (as a percent)									(11.10%)	(14.30%)	(33.60%)
Effect of domestic production activities (as a percent)									(0.00%)	(3.80%)	2.50%
Effect of change in U.S. tax law (as a percent)									1.50%	34.50%	0.00%
IRS and state tax examination settlements (as a percent)									0.00%	0.00%	21.50%
Effect of valuation allowance (as a percent)									(0.70%)	0.80%	0.00%
Research and development credit (as a percent)									(0.50%)	(0.00%)	(0.00%)
Non-controlling interest (as a percent)									(2.90%)	(0.00%)	(0.00%)
State rate change and prior period adjustments (as a percent)									(0.044)	0.000	0.000
Other (as a percent)									(0.60%)	(1.60%)	(4.50%)
Income Tax Expense / Effective Rate (as a percent)									4.80%	51.30%	22.40%