Annual report pursuant to Section 13 and 15(d)

Financial Instruments, Fair Value, and Concentrations of Credit Risk - Summary of Fair Value Measurements and Financial Statement Presentation (Detail)

v3.19.1
Financial Instruments, Fair Value, and Concentrations of Credit Risk - Summary of Fair Value Measurements and Financial Statement Presentation (Detail) - USD ($)
$ in Thousands
Dec. 31, 2018
Dec. 31, 2017
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]    
Fair Values of Assets $ 1 $ 3
Forward Purchase Contracts [Member]    
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]    
Fair Values of Assets 1 [1] 3 [2]
Fair Values of Liabilities 248 [1] 4 [2]
Level 2 [Member]    
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]    
Fair Values of Assets 1 3
Level 2 [Member] | Forward Purchase Contracts [Member]    
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]    
Fair Values of Assets 1 [1] 3 [2]
Fair Values of Liabilities $ 248 [1] $ 4 [2]
[1] The fair value for forward purchase contracts is estimated based on commodity futures market prices.
[2] The fair value for forward purchase contracts is estimated based on commodity market future prices.