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Organization and Significant Accounting Policies - Property Plant And Equipment Useful Lives (Parenthetical) (Detail)
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]      
Period over which internal use developed software costs are amortised 5 years 5 years 5 years