Stock-Based Compensation - Disclosures for 2004 Purchase Plan (Detail) - $ / shares	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Weighted-average purchase price per share	$ 341.48	$ 250.65	$ 217.91
Weighted average grant-date fair value per share of shares purchased	$ 90.04	$ 72.21	$ 60.49
Number of shares purchased	145,346	162,076	150,044

Number of shares issued during the period as a result of an employee stock purchase plan.

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Name:	us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration