Condensed Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Condensed Consolidated Balance Sheets [Abstract]
Accounts and notes receivable, allowances	$ 45,198	$ 43,958
Common stock, par value
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares outstanding	58,670,801	58,422,781