Consolidated Statements of Equity (USD $) In Thousands, unless otherwise specified	Common Shares	Additional Paid-in Capital	Treasury Shares	Accumulated Other Comprehensive Loss	Retained Earnings	Noncontrolling Interest [Member]	Total
Beginning Balance at Dec. 31, 2008	$ 96	$ 173,393	$ (16,737)	$ (30,046)	$ 226,707	$ 11,694	$ 365,107
Net income					38,351	1,215	39,566
Other comprehensive income:
Unrecognized actuarial loss (gain) and prior service costs (net of income tax of $10,293, $3,116 and $2,431 for 2011, 2010 and 2009, respectively)				4,491			4,491
Cash flow hedge activity (net of income tax of $21, $112, and $134 for 2011, 2010 and 2009, respectively)				241			241
Comprehensive income							44,298
Purchase of treasury shares (85 and 20 shares for 2011 and 2009 respectively)			(229)				(229)
Stock awards, stock option exercises, and other shares issued to employees and directors, net of income tax of $1,197, $1,076, and $826 for 2011, 2010 and 2009 respectively (150, 157 and 171 shares for 2011, 2010 and 2009 respectively)		2,084	1,412				3,496
Dividends declared ($0.4810, $0.3575 and $0.3475 per common share for 2011, 2010 and 2009 respectively)					(6,396)		(6,396)
Ending Balance at Dec. 31, 2009	96	175,477	(15,554)	(25,314)	258,662	12,909	406,276
Net income					64,662	219	64,881
Other comprehensive income:
Unrecognized actuarial loss (gain) and prior service costs (net of income tax of $10,293, $3,116 and $2,431 for 2011, 2010 and 2009, respectively)				(4,992)			(4,992)
Increase in estimated fair value of investment in debt securities (net of income tax of $1,710 and $1,004 for 2011 and 2010)				1,685			1,685
Cash flow hedge activity (net of income tax of $21, $112, and $134 for 2011, 2010 and 2009, respectively)				(178)			(178)
Comprehensive income							61,396
Stock awards, stock option exercises, and other shares issued to employees and directors, net of income tax of $1,197, $1,076, and $826 for 2011, 2010 and 2009 respectively (150, 157 and 171 shares for 2011, 2010 and 2009 respectively)		2,398	1,496				3,894
Dividends declared ($0.4810, $0.3575 and $0.3475 per common share for 2011, 2010 and 2009 respectively)					(7,007)		(7,007)
Ending Balance at Dec. 31, 2010	96	177,875	(14,058)	(28,799)	316,317	13,128	464,559
Net income					95,106	1,719	96,825
Other comprehensive income:
Unrecognized actuarial loss (gain) and prior service costs (net of income tax of $10,293, $3,116 and $2,431 for 2011, 2010 and 2009, respectively)				(17,120)			(17,120)
Increase in estimated fair value of investment in debt securities (net of income tax of $1,710 and $1,004 for 2011 and 2010)				2,860			2,860
Cash flow hedge activity (net of income tax of $21, $112, and $134 for 2011, 2010 and 2009, respectively)				(31)			(31)
Comprehensive income							82,534
Purchase of treasury shares (85 and 20 shares for 2011 and 2009 respectively)			(3,039)				(3,039)
Stock awards, stock option exercises, and other shares issued to employees and directors, net of income tax of $1,197, $1,076, and $826 for 2011, 2010 and 2009 respectively (150, 157 and 171 shares for 2011, 2010 and 2009 respectively)		1,588	2,100				3,688
Dividends declared ($0.4810, $0.3575 and $0.3475 per common share for 2011, 2010 and 2009 respectively)					(8,900)		(8,900)
Ending Balance at Dec. 31, 2011	$ 96	$ 179,463	$ (14,997)	$ (43,090)	$ 402,523	$ 14,847	$ 538,842