Declared Common Stock Dividends (Detail) (USD $)	3 Months Ended
	Mar. 31, 2015
Dividend Payment 1st
Dividends Payable [Line Items]
Declaration Date	Feb. 20, 2014
Record Date	Apr. 02, 2014
Payable Date	Apr. 15, 2014
Per Share	$ 0.51
Dividend Payment 2nd
Dividends Payable [Line Items]
Declaration Date	May 15, 2014
Record Date	Jul. 02, 2014
Payable Date	Jul. 15, 2014
Per Share	$ 0.51
Dividend Payment 3rd
Dividends Payable [Line Items]
Declaration Date	Aug. 14, 2014
Record Date	Oct. 02, 2014
Payable Date	Oct. 15, 2014
Per Share	$ 0.51
Dividend Payment 4th
Dividends Payable [Line Items]
Declaration Date	Dec. 11, 2014
Record Date	Jan. 02, 2015
Payable Date	Jan. 15, 2015
Per Share	$ 0.51
Dividend Payment 5th
Dividends Payable [Line Items]
Declaration Date	Feb. 20, 2015
Record Date	Apr. 02, 2015
Payable Date	Apr. 15, 2015
Per Share	$ 0.54