Treasury Stock - Additional Information (Detail) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended		81 Months Ended	1 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Nov. 07, 2014 Subsequent Event	Sep. 30, 2014 Maximum
Equity Class Of Treasury Stock [Line Items]
Common stock amount authorized under repurchase program, value	$ 99.2		$ 99.2		$ 99.2		$ 150.0
Stock repurchased during period, shares	174,310	0	174,310	641,300	5,724,664	432,417
Average stock price of shares repurchased	$ 15.75		$ 15.75	$ 11.56	$ 8.87	$ 16.78