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Summary of PSU Activity of the Incentive Plan (Detail) - Performance Share Units - $ / shares
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Number of Shares      
Number of Shares, beginning balance 453,748 150,980  
Granted 263,929 302,768 150,980
Number of Shares, ending balance 717,677 453,748 150,980
Weighted Average Grant Date Fair Value Per Share      
Weighted average fair value, Balance at beginning of period $ 7.04 $ 7.12  
Granted 8.35 7.00 $ 7.12
Weighted average fair value, Balance at end of period $ 7.52 $ 7.04 $ 7.12