Other Data (Details 1) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Characterization of distributions on common stock
Ordinary income per share	$ 0.63	$ 0.34	$ 0.40
Return of capital per share	$ 0.56	$ 0.80	$ 0.56
Unrecaptured section 1250 gain per share	$ 0.01	$ 0.06	$ 0.24
Common stock distributions per share	$ 1.20	$ 1.20	$ 1.20
Ordinary income in percent of common stock distribution	52.30%	28.50%	33.80%
Return of capital in percent of common stock distribution	47.10%	66.30%	46.40%
Unrecaptured section 1250 gain in percent of common stock distribution	0.60%	5.20%	19.80%
Common stock distribution in percentage	100.00%	100.00%	100.00%