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Mineral Rights, Net (Tables)
 3 Months Ended
Mar. 31, 2019
Extractive Industries [Abstract]  
Mineral Rights
The Partnership’s mineral rights consist of the following:
 
March 31, 2019
 
December 31, 2018
(In thousands)
Cost
 
Accumulated Depletion
 
Net Book Value
 
Cost
 
Accumulated Depletion
 
Net Book Value
Coal properties
$
1,164,845

 
$
(454,129
)
 
$
710,716

 
$
1,164,845

 
$
(451,210
)
 
$
713,635

Aggregates properties
24,920

 
(12,349
)
 
12,571

 
24,920

 
(11,814
)
 
13,106

Oil and gas royalty properties
12,395

 
(7,696
)
 
4,699

 
12,395

 
(7,632
)
 
4,763

Other
13,158

 
(1,574
)
 
11,584

 
13,158

 
(1,550
)
 
11,608

Total mineral rights, net
$
1,215,318

 
$
(475,748
)
 
$
739,570

 
$
1,215,318

 
$
(472,206
)
 
$
743,112