Income Taxes - Tax Status of Dividends (Details) - $ / shares	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Tax Disclosure [Abstract]
Document Fiscal Year Focus	2015
Dividend per share	$ 1.94	$ 1.88	$ 1.85
Ordinary income	71.00%	70.00%	70.00%
Capital gain	5.00%	16.00%	6.00%
Return of capital	19.00%	14.00%	0.00%
Allocation of Dividends, Qualified Dividend Income	5.00%	0.00%	24.00%