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Compensation Expense Associated with Performance Units (Detail) - Performance Units Awards - USD ($)
$ in Thousands
3 Months Ended 6 Months Ended
Jun. 30, 2020
Jun. 30, 2019
Jun. 30, 2020
Jun. 30, 2019
2020        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Stock-based compensation expense associated with Performance Units $ 69   $ 69  
2019        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Stock-based compensation expense associated with Performance Units 830 $ 830 1,660 $ 830
2018        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Stock-based compensation expense associated with Performance Units 667 667 1,334 1,334
2017        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Stock-based compensation expense associated with Performance Units $ 161 $ 482 $ 642 963
2016        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Stock-based compensation expense associated with Performance Units       $ 321