Dividends Declared Per Share (Detail) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Dividends Payable [Line Items]
Dividend Amount	$ 0.345	$ 0.345	$ 0.690	$ 1.035
Group One
Dividends Payable [Line Items]
Declaration Date			Jul. 22, 2014
Date Paid (Payable)			Aug. 29, 2014
Shareholder of Record Date			Aug. 15, 2014
Dividend Amount			$ 0.345
Group Two
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 Three
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 Four
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 Five
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 Six
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 Seven
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