Business Overview (Narrative) (Detail) (USD $)	9 Months Ended		1 Months Ended		9 Months Ended
	Sep. 30, 2012	Dec. 31, 2011	May 29, 2012 Barclays Bank PLC ("Barclays") [Member]	May 31, 2012 Barclays Bank PLC ("Barclays") [Member]	Sep. 30, 2012 Common Stock [Member]	Sep. 30, 2012 Convertible Preferred Stock [Member] Series B Preferred Stock [Member]	Sep. 30, 2012 Barclays [Member]	Sep. 30, 2012 Barclays [Member] Common Stock [Member]	Sep. 30, 2012 Voting Common Stock [Member]	Sep. 30, 2012 Nonvoting Common Stock [Member]
Schedule of Equity Method Investments [Line Items]
Common stock issued upon the conversion of Series B Convertible			26,211,335	26,211,335
Common stock, par value	$ 0.01	$ 0.01	$ 160.00	$ 160.00
Inclusion of shares of common stock issued upon the conversion of Series B Convertible Participating Preferred Stock			23,211,335
Repurchased shares from Barclays							6,377,552
Repurchased shares price							$ 156.80
Preferred shares						6,346,036
Shares repurchased from Barclays	1,858,100						35,210,021	31,516
Underwriters' option to purchase additional shares					2,621,134
Equity ownership percentage									21.00%	21.80%