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Stockholder's Equity - Long Term Incentive Plan Narrative (Detail) - Restricted Stock Units (RSUs) - shares
12 Months Ended 48 Months Ended 84 Months Ended
Dec. 31, 2020
Dec. 31, 2015
Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Awards returned during period (in shares) 407,217    
LTIP      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Restricted stock units ("RSUs") issued to directors and key employees (in shares)   1,013,000 1,078,000
RSU's Vested per performance criteria during period 8 years    
Number of cumulative total restricted shares, vested (in shares)     194,637
Awards returned during period (in shares) 818,363