Condensed Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Allowances for accounts and notes receivable	$ 1,591	$ 2,491
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	45,157,991	43,594,229
Common stock, shares outstanding	45,157,991	43,594,229
Voting common stock
Common stock, shares authorized	60,000,000	60,000,000
Common stock, shares issued	11,932,722	11,932,735
Common stock, shares outstanding	11,932,722	11,932,735