Incentive Compensation Plan - Unvested Target Award (Detail) - shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Outstanding, beginning of the year, Shares	231,834	265,000	271,000
Granted, Shares	121,348	135,370	94,626
Vested, Shares	(105,514)	(168,536)	(98,487)
Forfeited, Shares	0	0	(2,139)
Outstanding, end of the year, Shares	247,668	231,834	265,000
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Outstanding, beginning of the year, Shares	320,705	284,000	250,777
Granted, Shares	176,936	185,000	126,389
Vested, Shares	(18,348)	(34,200)	(12,626)
Forfeited, Shares	(52,697)	(114,095)	(80,540)
Outstanding, end of the year, Shares	426,596	320,705	284,000