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Shareholders' Equity and Share Based Compensation - Summary of Performance base restricted share unit activity (Detail) - Performance-Based Restricted Share Unit [Member]
3 Months Ended
Mar. 31, 2021
$ / shares
shares
Share Based Compensation Shares Authorized Under Stock Option Plans Exercise Price Range [Line Items]  
Number of Performance-based Restricted Share Units, Beginning balance | shares 869,000
Number of Performance-based Restricted Share Units, Received | shares (243,000)
Number of Performance-based Restricted Share Units, Ending balance | shares 626,000
Number of Performance-based Restricted Share Units, Exercisable | shares 5,000
Weighted Average Grant Date Fair Value, Beginning balance | $ / shares $ 7.51
Weighted Average Grant Date Fair Value, Received | $ / shares 6.53
Weighted Average Grant Date Fair Value, Ending balance | $ / shares 7.89
Weighted Average Grant Date Fair Value, Exercisable | $ / shares $ 5.79