Stock Compensation Plans - SSAR's and Stock Option Activity (Detail) - SSAR's and Stock Options [Member] - $ / shares shares in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Shares Subject to SSARs/Options
Beginning balance (in shares)	4
Granted (in shares)	9
Exercised (in shares)	(1)
Cancelled (in shares)	0
Ending balance (in shares)	12	4
Weighted Average Exercise Price
Beginning balance (in dollars per share)	$ 64.25
Granted (in dollars per share)	140.10
Exercised (in dollars per share)	60.39
Cancelled (in dollars per share)	0.00
Ending balance (in dollars per share)	$ 117.21	$ 64.25
SSARs/ Options Exercisable (in shares)	4	4