Stock-Based Compensation Plans - Restricted Stock and Performance Share Activity (Detail) - Restricted Stock [Member] - $ / shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Restricted Shares, Beginning balance	432,138	435,989	569,734
Number of Restricted Shares, Granted	95,419	117,668	149,349
Number of Restricted Shares, Performance share pay-out	61,936	117,647	46,340
Number of Restricted Shares, Canceled	(12,786)	(3,845)	(43,185)
Number of Restricted Shares, Vested	(192,729)	(235,321)	(286,249)
Number of Restricted Shares, Ending balance	383,978	432,138	435,989
Weighted Average Grant Date Fair Value, Beginning balance	$ 56.24	$ 41.83	$ 31.86
Weighted Average Grant Date Fair Value, Ending balance	$ 71.50	$ 56.24	$ 41.83