Stockholders' Equity (Tax Status of Distributions) (Details) - Common Stock - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Class of Stock [Line Items]
Tax Status of Common Stock Dividends Per Share Declared (in usd per share)	$ 0.240000	$ 2.853075	$ 0.320000
Unrecaptured Section 1250 Gain (in usd per share)	0.070522	0.100934	0.097271
Nondividend Distributions (in usd per share)	0.000000	2.190636	0.000000
AMT Adjustment (in usd per share)	0.017756	0.000000	0.000000
Ordinary Dividends
Class of Stock [Line Items]
Tax Status of Common Stock Dividends Per Share Declared (in usd per share)	0.093312	0.079661	0.161738
Long-Term Capital Gain
Class of Stock [Line Items]
Tax Status of Common Stock Dividends Per Share Declared (in usd per share)	$ 0.146688	$ 0.582778	$ 0.158262