Accounting Policies (Impairment & Other) (Details) (USD $)	12 Months Ended
	Dec. 31, 2014 segment	Dec. 31, 2013	Dec. 31, 2012
Deferred Financing Costs
Deferred financing costs, net of accumulated amortization	$ 60,328,000	$ 62,215,000
Amortized costs included in interest expense	16,900,000	13,500,000	10,500,000
Fair Values of Financial Instruments
Unit conversion factor for common stock	0.7866
Revenue Recognition
Straight-line rent receivables	187,969,000	150,829,000
Allowance for straight-line rent receivable	$ 145,100,000	$ 101,400,000
Term of resident lease agreements, minimum (in months)	12 months
Term of resident lease agreements, maximum (in months)	18 months
Notice period to cancel lease agreements by the resident (in days)	30 days
Segment Reporting
Number of reportable business segments	3