Dividends Declared Per Share (Detail) (USD $)	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Dividends Payable [Line Items]
Dividend Amount	$ 0.345	$ 0.690
Group One
Dividends Payable [Line Items]
Declaration Date	Apr. 22, 2014
Date Paid (Payable)	May 29, 2014
Shareholder of Record Date	May 15, 2014
Dividend Amount	$ 0.345
Group Two
Dividends Payable [Line Items]
Declaration Date	Jan. 16, 2014
Date Paid (Payable)	Feb. 28, 2014
Shareholder of Record Date	Feb. 14, 2014
Dividend Amount	$ 0.345
Group Three
Dividends Payable [Line Items]
Declaration Date	Sep. 18, 2013
Date Paid (Payable)	Nov. 15, 2013
Shareholder of Record Date	Nov. 01, 2013
Dividend Amount	$ 0.345
Group Four
Dividends Payable [Line Items]
Declaration Date	Jun. 05, 2013
Date Paid (Payable)	Aug. 15, 2013
Shareholder of Record Date	Aug. 01, 2013
Dividend Amount	$ 0.345
Group Five
Dividends Payable [Line Items]
Declaration Date	Mar. 28, 2013
Date Paid (Payable)	May 15, 2013
Shareholder of Record Date	May 01, 2013
Dividend Amount	$ 0.345
Group Six
Dividends Payable [Line Items]
Declaration Date	Jan. 17, 2013
Date Paid (Payable)	Feb. 15, 2013
Shareholder of Record Date	Feb. 01, 2013
Dividend Amount	$ 0.345