Capital Stock and Equity Compensation (Deferred Stock Units) (Detail) - Deferred Stock Units - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Awards Outstanding
Non-vested awards outstanding, beginning balance (in shares)	8,400	9,250	11,900
Awards granted (in shares)	5,950	8,400	9,250
Stock issued (in shares)	(7,200)	(9,250)	(11,900)
Non-vested awards outstanding, ending balance (in shares)	7,150	8,400	9,250
Weighted- Average Grant Date Fair Value
Weighted-Average Grant Date Fair Value, Outstanding at period beginning (in dollars per share)	$ 108.86	$ 109.48	$ 58.82
Weighted-Average Grant Date Fair Value, Awards granted (in dollars per share)	183.40	108.86	109.48
Weighted-Average Grant Date Fair Value, Stock issued (in dollars per share)	108.86	109.48	58.82
Weighted-Average Grant Date Fair Value, Outstanding at period end (in dollars per share)	$ 170.89	$ 108.86	$ 109.48