Fair Value Measurements - Level 3 Inputs (Details)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Minimum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Long-term Revenue Growth Rate	(8.30%)	2.00%
Fair Value Inputs, Discount Rate	10.50%	8.50%
Maximum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Long-term Revenue Growth Rate	2.50%	3.00%
Fair Value Inputs, Discount Rate	10.50%	10.00%
Overall Cap Rate [Member] | Minimum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Cap Rate	8.30%	7.50%
Overall Cap Rate [Member] | Maximum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Cap Rate	8.50%	9.00%
Terminal Cap Rate [Member] | Minimum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Cap Rate	8.80%	8.00%
Terminal Cap Rate [Member] | Maximum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Inputs, Cap Rate	8.80%	9.50%