Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Allowances for accounts and notes receivable	$ 2,491	$ 1,885
Preferred stock, par value (USD per share)	$ 0.01	$ 0.01
Preferred stock, shares authorized	25,000,000	25,000,000
Preferred stock, shares outstanding	0	0
Common stock, par value (USD per share)	$ 0.01	$ 0.01
Common stock, Class A
Common stock, shares authorized	240,000,000	240,000,000
Common stock, shares issued	43,594,229	42,353,882
Common stock, shares outstanding	43,594,229	42,353,882
Voting common stock
Common stock, shares authorized	60,000,000	60,000,000
Common stock, shares issued	11,932,735	11,932,735
Common stock, shares outstanding	11,932,735	11,932,735