Annual report pursuant to Section 13 and 15(d)

Summary of Common Units Received Under Adjustment Agreement (Detail)

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Summary of Common Units Received Under Adjustment Agreement (Detail) - USD ($)
$ in Thousands
3 Months Ended 12 Months Ended
Mar. 31, 2019
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Schedule Of Equity Method Investments [Line Items]        
Number of Common Units Received 219,056      
Fair Value of Common Units Received $ 1,552 $ 1,552 $ 5,012 $ 18,363
Annual Common Unit Adjustment        
Schedule Of Equity Method Investments [Line Items]        
Date Common Units Received   Mar. 31, 2019 Mar. 29, 2018 Mar. 31, 2017
Number of Common Units Received   219,056 908,042 1,487,218
Fair Value of Common Units Received   $ 1,552 $ 5,012 $ 18,363