Treasury Stock - Additional Information (Detail) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended		87 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2015
Equity Class Of Treasury Stock [Line Items]
Common stock amount authorized under repurchase program, value	$ 94.7		$ 94.7
Stock repurchased during period, shares	96,277	0	5,987,849
Average stock price of shares repurchased	$ 17.66		$ 9.23
Maximum
Equity Class Of Treasury Stock [Line Items]
Common stock amount authorized under repurchase program, value	$ 150.0		$ 150.0