Dividends - Dividends Declared and Paid or Payable (Detail) (USD $)	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012
Dividend per Share	$ 0.18	$ 0.18
Dividend 1 [Member]
Date Declared	Jan. 29, 2013	Jan. 31, 2012
Record Date	Feb. 08, 2013	Feb. 10, 2012
Payment Date	Feb. 15, 2013	Feb. 15, 2012
Dividend per Share	$ 0.06	$ 0.06
Dividend 2 [Member]
Date Declared	Apr. 23, 2013	Apr. 19, 2012
Record Date	May 03, 2013	Apr. 30, 2013
Payment Date	May 15, 2013	May 15, 2012
Dividend per Share	$ 0.06	$ 0.06
Dividend 3 [Member]
Date Declared	Jul. 17, 2013	Jul. 19, 2012
Record Date	Jul. 30, 2013	Jul. 30, 2012
Payment Date	Aug. 15, 2013	Aug. 15, 2012
Dividend per Share	$ 0.06	$ 0.06