Schedule of Common Stock Repurchases (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Schedule Of Common Share Purchase [Line Items]
Shares repurchased	822,849	29,704	142,186
Cost of shares repurchased (in millions)	$ 491,633	$ 16,048	$ 68,320
Average price per share repurchased	$ 597.48	$ 540.25	$ 480.49

Equity impact of the cost of common and preferred stock that were repurchased during the period. Recorded using the cost method.

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