Incentive and Restricted Stock Plan and Dividend Reinvestment Plan - Summary of Nonstatutory Stock Options Activity (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Nonstatutory Stock Option Activity (shares) [Roll Forward]
Outstanding, Beginning of year	428,900	675,500	757,050
Granted	0	0	0
Exercised	0	0	0
Forfeited	(273,400)	(246,600)	(81,550)
Outstanding, End of year	155,500	428,900	675,500
Number of Shares Exercisable, End of year	155,500	428,900	675,500
Nonstatutory Stock Options, Outstanding, Weighted Average Exercise Price (dollars per share) [Abstract]
Beginning of year	$ 37.36	$ 35.18	$ 34.33
Granted	$ 0	$ 0	$ 0.00
Exercised	$ 0	$ 0	$ 0
Forfeited	$ 37.08	$ 31.39	$ 27.29
End of year	$ 37.86	$ 37.36	$ 35.18
Exercisable at End of Year	$ 37.86	$ 37.36	$ 35.18
Weighted Average Remaining Contractual Term, Outstanding	1 year	1 year 4 months 24 days	2 years
Weighted Average Remaining Contractual Term, Exercisable	1 year	1 year 4 months 24 days	2 years