Capital Stock - Summary Changes in Common Shares Outstanding (Detail) - shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Equity [Abstract]
Common Shares Outstanding, Beginning Balance	94,461,576	93,622,934	96,380,102
Issuance of restricted stock and restricted stock units		564,729	589,736
Issuance of stock as part of debt refinancing	15,942,551
Treasury stock purchases	(21,685)	(15,679)	(3,785,658)
Issuance of shares to directors	81,843		13,249
Vesting of restricted stock and restricted stock units	203,328	74,292
Exercise of stock options	114,000	215,300	425,505
Common Shares Outstanding, Ending Balance	110,781,613	94,461,576	93,622,934