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Common Stock - Summary of Information Regarding Outstanding SARs (Detail) - Stock Appreciation Rights (SARs) [Member] - $ / shares
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Restricted Shares Outstanding, Beginning balance 1,330,257 1,399,302
Granted 7,912 7,088
Forfeited (103,604) (76,133)
Restricted Shares Outstanding, Ending balance 1,234,565 1,330,257
Exercisable at end of year 1,219,555 1,315,701
Weighted-Average Grant Date Fair Value of Restricted Stock, Beginning Balance $ 28.45 $ 28.49
Granted 20.23 28.72
Forfeited 28.38 29.18
Weighted-Average Grant Date Fair Value of Restricted Stock, Ending Balance 28.40 28.45
Average Exercise Price, Exercisable at end of year $ 28.44 $ 28.40