Common Shares and Preferred Shares Common shares outstanding (Details) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Preferred shares
Preferred stock, shares authorized	4,000,000
Preferred stock, par value	$ 0
Preferred stock, shares issued	0
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Common stock, shares authorized	24,000,000	24,000,000
Common stock, par value	$ 1.00	$ 1.00
Common stock, shares issued	21,456,880	21,456,880	21,456,880
Treasury stock, shares	8,018,269	7,730,878	7,611,245
Common shares, direct sales	16,095
Common shares, value, direct sales	$ 374
Stock issued during period, shares, employee retirement plan	51,099
Stock issued during period, value, employee retirement plan	1,187
Common shares, employer matching contribution, shares	113,692
Employee Retirement Plan, Employer Match	2,788	2,643	2,473
Stock issued during period, shares, employee stock purchase plan	118,444
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares outstanding, beginning of year	13,726,002	13,845,635
Shares purchased	(931,078)	(891,704)
Shares sold	299,330	327,442
Stock subscription offering, employee cash purchases	25,837	76,525
Options exercised	318,520	368,104
Increase/(decrease) in shares outstanding	(287,391)	(119,633)
Shares outstanding, end of year	13,438,611	13,726,002	13,845,635
Per Share Amounts and Common Shares Outstanding [Abstract]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Number	342,146
Stock subscription offering, number of partially-paid subscriptions	531,325
Stock subscription offering, number of rights outstanding	204,972
Treasury Stock [Member]
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Shares purchased, value	$ 21,887	$ 18,103	$ 14,222
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares purchased	(931,000)	(892,000)	(779,000)
Shares sold	299,000	327,000	351,000