Treasury Stock - Additional Information (Detail) (USD $) In Millions, except Share data, unless otherwise specified	1 Months Ended	3 Months Ended		6 Months Ended		78 Months Ended
	Jun. 30, 2014	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014
Equity Class Of Treasury Stock [Line Items]
Common stock amount authorized under repurchase program, value	$ 109.2			$ 150.0
Stock repurchased during period, shares		0	480,100	0	641,300	5,117,937
Average stock price of shares repurchased			$ 11.04		$ 11.56	$ 7.97