Stock-Based Compensation Plans - Restricted Stock and Performance Share Activity (Detail) - Restricted Stock [Member] - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Restricted Shares, Beginning balance	271,870	319,599	383,978
Number of Restricted Shares, Granted	118,632	59,179	61,434
Number of Restricted Shares, Performance share pay-out	87,163	8,094	21,422
Number of Restricted Shares, Canceled	(2,321)	(4,046)	(4,590)
Number of Restricted Shares, Vested	(129,312)	(110,956)	(142,645)
Number of Restricted Shares, Ending balance	346,032	271,870	319,599
Weighted Average Grant Date Fair Value, Beginning balance	$ 112.47	$ 88.77	$ 71.50
Weighted Average Grant Date Fair Value, Ending balance	$ 154.27	$ 112.47	$ 88.77