Preferred Stock - Additional Information (Detail) (USD $)	0 Months Ended
	Mar. 20, 2015	Mar. 05, 2015	Mar. 31, 2015	Dec. 31, 2014
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
Series A Preferred Stock
Class of Stock [Line Items]
Dividend paid per share (usd per share)	$ 977.78
Preferred stock, dividend rate per normal preferred capital security (usd per share)	$ 9.7778
Dividends payable, date of record		Mar. 05, 2015
Preferred stock dividend payment date	Mar. 20, 2015
Depository share, portion of preferred stock share (percent)		1.00%
Series C Noncumulative Perpetual Preferred Stock
Class of Stock [Line Items]
Dividend paid per share (usd per share)	$ 1,300
Preferred stock, dividend rate per depository share (usd per share)	$ 0.3250
Dividends payable, date of record		Mar. 05, 2015
Preferred stock dividend payment date	Mar. 20, 2015
Depository share, portion of preferred stock share (percent)		0.025%