Condensed Consolidated Balance Sheet (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Trade receivables, allowance for doubtful accounts	$ 7,476	$ 7,402
Property, accumulated depreciation	$ 318,479	$ 310,279
Common stock, par value	$ 0	$ 0
Common stock, shares issued	62,081,391	62,081,391
Common stock, shares outstanding	37,167,717	37,007,799
Stock compensation trust, shares	359,201	745,430
Preferred Stock, 4 1/2% Cumulative
Percentage of cumulative preferred stock	4.50%	4.50%
Preferred stock, shares authorized	100,000	100,000
Preferred stock, par value	$ 50	$ 50
Preferred stock, shares issued	71,373	71,373
Preferred stock, callable per share	$ 52.50	$ 52.50
Treasury shares, at cost	52,878	52,878
Second Cumulative Preferred Voting Stock
Preferred stock, shares authorized	1,000,000	1,000,000
Preferred stock, par value	$ 10	$ 10
Preferred stock, shares issued	0	0
Common Stock
Treasury shares, at cost	24,554,473	24,328,162