Income Taxes (Tables)

12 Months Ended

Dec. 31, 2012

Income Taxes [Abstract]

Summary of taxability of cash distributions paid on common shares

For federal income tax purposes, the following summarizes the taxability of cash distributions paid on the common shares in 2011 and 2010 and the estimated taxability for 2012: 

	2012		2011		2010
Per common share
Ordinary income	$	2.16	$	1.90	$	1.64
Capital gains	0.48		0.33		—
Return of capital	—		0.28		0.82
Total	$	2.64	$	2.51	$	2.46