Preferred Stock - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Changes In Equity And Comprehensive Income Line Items [Line Items]
Convertible preferred stock par value	$ 50	$ 50
Noncumulative stock dividend	$ 5.00	$ 5.00
Holders of preferred stock entitled	One vote per share
Holders of common stock entitled	One vote per share
Noncumulative Preferred Stock [Member]
Changes In Equity And Comprehensive Income Line Items [Line Items]
Noncumulative stock dividend	$ 5.00
Number of shares of common stock	100