Capital Stock - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Capital Unit [Line Items]
Preferred stock, par value (dollars per share)	$ 50	$ 50
Percentage of cumulative preferred stock	4.50%	4.50%
Treasury shares, at cost	$ 295,070,000	$ 286,557,000
Common stock, shares authorized	180,000,000	180,000,000
Common stock, par value (dollars per share)	$ 0	$ 0
Common stock, shares outstanding	37,372,474	37,448,310
4 1/2% Cumulative Preferred Nonvoting Stock
Capital Unit [Line Items]
Preferred stock, shares authorized	100,000
Preferred stock, par value (dollars per share)	$ 50
Percentage of cumulative preferred stock	4.50%
Preferred stock, callable price per share (dollars per share)	$ 52.50
Preferred stock, shares issued	71,340
Treasury share, number of shares held	52,878
Treasury Stock, Shares, Retired	33
Purchase of treasury shares		0	0
Treasury shares, at cost	$ 1,800,000
Second Cumulative Preferred Voting Stock
Capital Unit [Line Items]
Preferred stock, shares authorized	1,000,000
Preferred stock, par value (dollars per share)	$ 10
Preferred stock, shares issued	0	0
Common Stock
Capital Unit [Line Items]
Common stock, shares outstanding	62,081,391	62,081,391	62,081,391	62,081,391
Share Repurchase Program, May 2015 | Common Stock
Capital Unit [Line Items]
Purchase of treasury shares	150,000
Stock repurchased program, authorized amount (up to)	$ 100,000,000