Borrowings (Indebtedness) (Details) (USD $)	12 Months Ended		12 Months Ended									12 Months Ended			12 Months Ended						12 Months Ended								12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2013 Secured Debt	Dec. 31, 2013 Unsecured Debt	Dec. 31, 2013 Interest Rate Forward Swap Contract	Oct. 16, 2013 Interest Rate Forward Swap	Oct. 16, 2013 Senior Notes Unsecured Debt	Dec. 31, 2013 FNMA	Dec. 31, 2013 FNMA Secured Debt	Dec. 31, 2013 Fixed Rate Debt	Dec. 31, 2012 Fixed Rate Debt	Dec. 31, 2013 Fixed Rate Debt Secured Debt	Dec. 31, 2013 Fixed Rate Debt Unsecured Debt	Dec. 31, 2012 Fixed Rate Debt Unsecured Debt	Dec. 31, 2013 Fixed Rate Debt Individual Property Mortgages Secured Debt	Dec. 31, 2013 Fixed Rate Debt LIBOR-based interest rate swaps Secured Debt	Dec. 31, 2013 Fixed Rate Debt Term loan fixed with swaps Unsecured Debt	Dec. 31, 2013 Fixed Rate Debt Senior Notes Unsecured Debt	Dec. 31, 2013 Variable Rate Debt	Dec. 31, 2012 Variable Rate Debt	Dec. 31, 2013 Variable Rate Debt Secured Debt		Dec. 31, 2013 Variable Rate Debt Unsecured Debt		Dec. 31, 2012 Variable Rate Debt Unsecured Debt		Dec. 31, 2013 Variable Rate Debt Mortgages Secured Debt		Dec. 31, 2013 FNMA Fixed Rate Debt Conventional Credit Facility Secured Debt	Dec. 31, 2013 FNMA Variable Rate Debt Conventional Credit Facility Secured Debt		Dec. 31, 2013 FNMA Variable Rate Debt Tax Free Credit Facility Secured Debt		Dec. 31, 2013 Freddie Mac Variable Rate Debt Conventional Credit Facility Secured Debt		Dec. 31, 2013 Freddie Mac Variable Rate Debt Mortgages Secured Debt		Dec. 31, 2013 Interest Rate Cap FNMA Contract	Dec. 31, 2013 Interest Rate Swap FNMA Contract	Dec. 31, 2013 Minimum	Dec. 31, 2013 Minimum Interest Rate Cap FNMA	Dec. 31, 2013 Minimum Interest Rate Swap FNMA	Dec. 31, 2013 Maximum	Dec. 31, 2013 Maximum Interest Rate Cap FNMA	Dec. 31, 2013 Maximum Interest Rate Swap FNMA
Debt Instrument [Line Items]
Notional amount of interest rate derivatives					$ 150,000,000																																	$ 273,000,000	$ 125,000,000
Line of credit facility, maximum borrowing capacity	500,000,000								453,500,000
Line of credit average interest rate	1.10%
Derivative instrument maturity year																																									2014	2014		2018	2015
Basis spread on variable rate									0.17%																															0.90%			1.70%
Total outstanding debt	3,472,718,000	1,673,800,000	1,790,935,000	1,681,783,000						3,062,600,000	1,291,400,000	1,380,812,000	1,131,800,000	310,000,000	1,111,812,000	219,000,000	550,000,000	1,131,783,000	410,100,000	382,400,000	410,123,000	[1]	0	[2]	23,000,000	[2]	27,342,000	[1]	50,000,000	189,721,000	[1]	88,812,000	[1]	104,248,000	[1]
Average interest rate (percentage)	3.90%	3.80%	3.50%	4.30%		4.15%						4.20%			4.00%	5.30%	3.10%	5.00%			1.00%	[1]					3.30%	[1]	4.70%	0.80%	[1]	0.90%	[1]	0.70%	[1]
Number of Interest rate derivatives held					3																																	22	4
Contract maturity	Apr. 28, 2018		Sep. 01, 2018	Feb. 12, 2019								Jun. 13, 2018			Apr. 01, 2013	Aug. 31, 2014	Nov. 10, 2017	Sep. 22, 2019			May 27, 2019	[1]							Mar. 31, 2017	Dec. 02, 2016	[1]	Jul. 23, 2031	[1]	Jul. 01, 2014	[1]	Oct. 31, 2015	[1]
Long-term Debt, Percentage Bearing Variable Interest, Percentage Rate								0.80%
Line of credit facility, amount outstanding	0							453,500,000
Debt instrument, face amount							350,000,000
Interest rate, stated percentage							4.30%																1.46%	[2]
Debt instrument, issue price							$ 0.99047

[1] Includes capped balances

[2] Amounts are adjusted to reflect interest rate swap and cap agreements in effect at December 31, 2013, and 2012, respectively, which results in the Company paying fixed interest payments over the terms of the interest rate swaps and on changes in interest rates above the strike rate of the cap.