Subsidiary Preferred Stock (Details) (Superior subsidiary, USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012 item
Subsidiary preferred stock
Subsidiary Preferred Stock, par value (in dollars per share)	$ 0.01
Subsidiary Preferred Stock, shares authorized	10,000,000
Cumulative dividends per annum on preferred stock (in dollars per share)	$ 40.00
Liquidation value (in dollars per share)	$ 1,000
Liquidation preference (in dollars)	$ 75.0
Redemption price of preferred stock (as a percent)	101.00%
Conversion price of preferred stock into Superior common stock (in shares)	22.12
Conversion price of preferred stock (in dollars per share)	$ 25.00
Conversion rate of preferred stock into deemed common shares (in shares)	40
Number of deemed common shares in conversion	3,000,000
Redemption value of preferred stock	$ 66.4
Number of voter per share entitled under preferred stock voting rights	1
Series A Preferred Stock
Subsidiary preferred stock
Subsidiary preferred stock, shares outstanding	75,000