Employee Benefit Plans - Summary of Activity for the Stock Option Component of the Incentive Plan (Detail)	12 Months Ended
	Dec. 31, 2016 $ / shares shares
Compensation Related Costs [Abstract]
Number of options, Outstanding at beginning of the year | shares	287,500
Number of options, Granted during the year | shares	96,600
Number of options, Exercised during the year | shares	(101,190)
Number of options, Forfeited or expired during the year | shares	(6,788)
Number of options, Outstanding at end of the year | shares	276,122
Number of options, Exercisable at year end | shares	228,272
Weighted average exercise price per share, Outstanding at beginning of the year | $ / shares	$ 27.02
Weighted average exercise price per share, Granted during the year | $ / shares	32.37
Weighted average exercise price per share, Exercised during the year | $ / shares	24.58
Weighted average exercise price per share, Forfeited or expired during the year | $ / shares	30.09
Weighted average exercise price per share, Outstanding at end of the year | $ / shares	29.71
Weighted average exercise price per share, Exercisable at year end | $ / shares	$ 29.15