Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2017	Dec. 31, 2016
Federal:
Current	$ 27,877	$ 15,657	$ 4,810
Deferred	(4,397)	9,919	25,955
Total federal	23,480	25,576	30,765
State:
Current	5,520	4,567	1,914
Deferred	(338)	19	2,500
Total state	5,182	4,586	4,414
Provision for income taxes	28,662	30,162	35,179
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Federal statutory tax	36,562	33,728	35,165
State taxes, net of federal tax benefit	3,814	2,990	3,769
Percentage depletion deduction	(1,368)	(1,352)	(1,444)
Domestic production deduction	(2,765)	(1,624)	(306)
Noncontrolling interests	(2,346)	(3,177)	(2,639)
Nondeductible expenses	1,128	1,094	219
Tax Cuts and Jobs Act of 2017	(3,664)	0	0
Other	(2,699)	(1,497)	415
Provision for income taxes	$ 28,662	$ 30,162	$ 35,179
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Federal statutory tax, Percent	35.00%	35.00%	34.00%
State taxes, net of federal tax benefit, Percent	3.70%	3.10%	3.60%
Percentage depletion deduction, Percent	(1.30%)	(1.40%)	(1.40%)
Domestic production deduction, Percent	(2.70%)	(1.70%)	(0.30%)
Non-controlling interests, Percent	(2.30%)	(3.30%)	(2.60%)
Nondeductible expenses, Percent	1.10%	1.10%	0.20%
Tax Cuts and Jobs Act of 2017, Percent	(3.50%)	0.00%	0.00%
Other, Percent	(2.60%)	(1.50%)	0.50%
Total, Percent	27.40%	31.30%	34.00%
Deferred tax assets:
Receivables				$ 526	$ 573
Inventory				1,513	2,212
Insurance				7,401	12,524
Deferred compensation				8,985	12,740
Other accrued liabilities				1,525	2,294
Accrued compensation				1,738	11,031
Other				1,379	2,481
Net operating loss carryforward				2,614	2,341
Valuation allowance	$ 2,153	$ 641	$ 1,185	2,471	2,153
Total deferred tax assets				23,210	44,043
Deferred tax liabilities:
Property and equipment				16,832	29,400
Contract income recognition				7,739	20,084
Total long-term deferred tax liabilities				24,571	49,484
Deferred Tax Liabilities, Tax Deferred Income				1,361	5,441
Deferred Tax Assets, Valuation Allowance [Roll Forward]
Beginning balance	2,153	641	1,185
Additions (deductions), net	318	1,512	(544)
Ending balance	2,471	2,153	641
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Beginning balance	3,300
Ending balance	3,200	3,300
Unrecognized Tax Benefits	3,300	3,300		3,200	3,300
Unrecognized Tax Benefits that Would Impact Effective Tax Rate				3,100	3,200
Unrecognized Tax Benefits, Interest on Income Taxes Expense	200	(100)	100
Unrecognized Tax Benefits, Interest on Income Taxes Accrued				400	200
Other Long Term Liabilities [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Beginning balance	3,262	1,578	887
Gross increases – current period tax positions	0	1,902	1,006
Gross decreases – current period tax positions	(73)	(125)	(156)
Gross increases – prior period tax positions	1	2	0
Gross decreases – prior period tax positions	(6)	(5)	0
Settlements with taxing authorities/lapse of statute of limitations	(13)	(90)	(159)
Ending balance	3,171	3,262	1,578
Unrecognized Tax Benefits	$ 3,262	$ 1,578	$ 887	$ 3,171	$ 3,262