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Derivatives Hedges and Financial Instruments - Additional Information (Detail)
$ / shares in Units, MMBTU in Millions, $ in Millions
3 Months Ended 12 Months Ended
Mar. 31, 2020
USD ($)
MMBTU
$ / shares
$ / MMBTU
shares
Mar. 31, 2019
USD ($)
Dec. 31, 2019
MMBTU
$ / shares
shares
Derivative Instruments And Hedging Activities Disclosures [Line Items]      
Loss on sale of natural gas | $ $ (0.7)    
Unrealized loss on sale of natural gas | $ (0.5) $ 0.0  
Non-Operating Other Income [Member]      
Derivative Instruments And Hedging Activities Disclosures [Line Items]      
Unrealized gain (loss) on fair value of embedded derivative | $ $ 0.6 $ (0.2)  
Embedded Derivative [Member]      
Derivative Instruments And Hedging Activities Disclosures [Line Items]      
Participating right in dividends and liquidating distributions expressed in number of common shares | shares 303,646   303,646
Embedded Derivative [Member] | Common Stock Shares [Member]      
Derivative Instruments And Hedging Activities Disclosures [Line Items]      
Common stock per share | $ / shares $ 2.10   $ 4.20
Natural Gas Purchase Commitments [Member]      
Derivative Instruments And Hedging Activities Disclosures [Line Items]      
Natural gas purchase commitments volume | MMBTU 11.5    
Weighted average cost of natural gas per unit 1.85    
Weighted average natural gas market value per unit 1.75    
Natural Gas Purchase Commitments [Member] | Level 2 [Member]      
Derivative Instruments And Hedging Activities Disclosures [Line Items]      
Natural gas purchase commitments volume | MMBTU 2.6   0.0
Weighted average cost of natural gas per unit 2.01    
Weighted average natural gas market value per unit 1.81