Preferred stock- Additional Information (Detail) (USD $)			0 Months Ended		9 Months Ended
	Sep. 30, 2014	Dec. 31, 2013	Sep. 22, 2014 Series A Preferred Stock	Sep. 22, 2014 Series C Noncumulative Perpetual Preferred Stock	Sep. 30, 2014 Series C Noncumulative Perpetual Preferred Stock
Class of Stock [Line Items]
Preferred stock, shares authorized (shares)	100,000,000	100,000,000
Preferred stock, par value (usd per share)	$ 0.01	$ 0.01
Dividend paid per share (usd per share)			$ 1,044.44	$ 1,300.00
Preferred Stock, Dividend Rate, Per Normal Preferred Capital Security			$ 10.4444
Preferred Stock, Dividend Rate, Per Depositary Share				$ 0.3250
Preferred stock redemption period following regulatory capital treatment event					90 days