Condensed Consolidated Statements of Equity (Unaudited) (USD $) In Thousands, unless otherwise specified	Total	Common Shares	Additional Paid-in Capital	Treasury Shares	Accumulated Other Comprehensive Loss	Retained Earnings	Noncontrolling Interest
Beginning Balance at Dec. 31, 2010	$ 464,559	$ 96	$ 177,875	$ (14,058)	$ (28,799)	$ 316,317	$ 13,128
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	63,423					62,484	939
Other comprehensive income	(668)				(668)
Purchase of treasury shares (4 shares)	(140)			(140)
Stock awards, stock option exercises and other shares issued to employees and directors, net of income tax of $675 (140 shares) and $1,199 (133 shares) for the year June 30, 2012 and 2011, respectively	1,375		(609)	1,984
Dividends declared ($0.30 and $0.22 per common share for the year June 30, 2012 and 2011, respectively)	(4,086)					(4,086)
Ending Balance at Jun. 30, 2011	524,463	96	177,266	(12,214)	(29,467)	374,715	14,067
Beginning Balance at Dec. 31, 2011	538,842	96	179,463	(14,997)	(43,090)	402,523	14,847
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	46,199					47,606	(1,407)
Other comprehensive income	92				92
Proceeds received from minority investor	6,100						6,100
Stock awards, stock option exercises and other shares issued to employees and directors, net of income tax of $675 (140 shares) and $1,199 (133 shares) for the year June 30, 2012 and 2011, respectively	3,550		1,072	2,478
Dividends declared ($0.30 and $0.22 per common share for the year June 30, 2012 and 2011, respectively)	(5,590)					(5,590)
Ending Balance at Jun. 30, 2012	$ 589,193	$ 96	$ 180,535	$ (12,519)	$ (42,998)	$ 444,539	$ 19,540