Declared Common Stock Dividends (Detail) - $ / shares	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Dividends Payable [Line Items]
Per Share	$ 0.54	$ 0.54
Dividend Payment 1st
Dividends Payable [Line Items]
Declaration Date	Feb. 20, 2015
Record Date	Apr. 02, 2015
Payable Date	Apr. 15, 2015
Per Share	$ 0.54
Dividend Payment 2nd
Dividends Payable [Line Items]
Declaration Date	May 14, 2015
Record Date	Jul. 02, 2015
Payable Date	Jul. 15, 2015
Per Share	$ 0.54
Dividend Payment 3rd
Dividends Payable [Line Items]
Declaration Date	Aug. 13, 2015
Record Date	Oct. 02, 2015
Payable Date	Oct. 15, 2015
Per Share	$ 0.54
Dividend Payment 4th
Dividends Payable [Line Items]
Declaration Date	Dec. 10, 2015
Record Date	Jan. 04, 2016
Payable Date	Jan. 15, 2016
Per Share	$ 0.54
Dividend Payment 5th
Dividends Payable [Line Items]
Declaration Date	Feb. 19, 2016
Record Date	Apr. 01, 2016
Payable Date	Apr. 15, 2016
Per Share	$ 0.54