Notes and Bonds Payable (Details Textuals) (USD $)	6 Months Ended			6 Months Ended		1 Months Ended	6 Months Ended		6 Months Ended			6 Months Ended		6 Months Ended			6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Dec. 31, 2010	Jun. 30, 2011 Unsecured Credit Facility due 2012 [Member]	Dec. 31, 2010 Unsecured Credit Facility due 2012 [Member]	Mar. 31, 2011 Senior Notes Due 2011 [Member]	Jun. 30, 2011 Senior Notes Due 2011 [Member]	Mar. 28, 2011 Senior Notes Due 2011 [Member]	Jun. 30, 2011 Senior Notes Due 2014 [Member]	Dec. 31, 2010 Senior Notes Due 2014 [Member]	Dec. 31, 2004 Senior Notes Due 2014 [Member]	Jun. 30, 2011 Senior Notes Due 2017 [Member]	Dec. 31, 2010 Senior Notes Due 2017 [Member]	Jun. 30, 2011 Senior Notes Due 2021 [Member]	Dec. 31, 2010 Senior Notes Due 2021 [Member]	Dec. 30, 2010 Senior Notes Due 2021 [Member]	Jun. 30, 2011 Contractual interest rates [Member]	Jun. 30, 2011 Mortgage Notes 7.765% [Member] Life Insurance Co [Member]	Jun. 30, 2011 Mortgage Notes 5.550% [Member] Commercial Bank [Member]	Jun. 30, 2011 Mortgage Notes 5.490% [Member] Life Insurance Co [Member]	Jun. 30, 2011 Mortgage Notes 6.480% [Member] Commercial Bank [Member]	Jun. 30, 2011 Mortgage Notes 6.110% [Member] Commercial Bank [Member]	Jun. 30, 2011 Mortgage Notes 7.650% [Member] Commercial Bank [Member]	Jun. 30, 2011 Mortgage Notes 6.810% [Member] Life Insurance Co [Member]	Jun. 30, 2011 Mortgage Notes 6.430% [Member] Commercial Bank [Member]	Jun. 30, 2011 Mortgage Notes 7.250% [Member] Investment Fund [Member]	Jun. 30, 2011 Mortgage Notes 5.530% [Member] Life Insurance Co [Member]	Jun. 30, 2011 Mortgage Notes 6.550% [Member] Investment Co [Member]	Jun. 30, 2011 Investment Co [Member]
Debt Instrument [Line Items]
Amended and restated unsecured credit facility				$ 550,000,000
Syndicate of lenders				16
Interest rate terms for unsecured credit facility				Rate equal to (x) LIBOR or the base rate (defined as the highest of (i) the Federal Funds Rate plus 0.5%; (ii) the Bank of America prime rate and (iii) LIBOR) plus (y) a margin ranging from 2.15% to 3.20% (currently 2.80% at June 30, 2011) for LIBOR-based loans and 0.90% to 1.95% for base rate loans ( 1.55% at June 30,2011), based upon the Company’s unsecured debt ratings
Facility fee on the aggregate amount of commitments				0.40%
Facility fee if credit rating falls below a BBB-/Baa3				0.50%
Amount outstanding under Unsecured Credit Facility				123,000,000	0
Weighted average interest rate (LOC)				29.90%
Remaining borrowing capacity				427,000,000
Public Issue of Unsecured senior notes									264,737,000	264,737,000	300,000,000	300,000,000	300,000,000	400,000,000	400,000,000	400,000,000		4,700,000	1,800,000	15,100,000	17,400,000	12,000,000	15,200,000	1,500,000	12,900,000	80,000,000	7,000,000	15,900,000
Interest rate on senior notes							8.125%		5.125%		5.125%	6.50%		5.75%
Discount on notes issued									439,000	510,000	1,500,000	1,660,000	1,782,000	3,070,000	3,188,000	3,200,000					2,700,000	2,100,000	2,400,000	200,000	1,000,000
Interest rate yielded per annum upon issuance											5.19%	6.618%			5.855%			7.765%	5.55%	5.49%	6.48%	6.11%	7.65%	6.81%	6.43%	7.25%	5.53%	6.55%
Amount of amortization included in interest expense on the Company,s consolidated Statements of operations	100,000
Redemption of unsecured senior notes						289,400,000
Outstanding principal of unsecured senior notes						278,200,000
Accrued interest	66,768,000		62,652,000
Accrued interest								9,200,000
Early extinguishment of the debt	(1,986,000)	(480,000)					2,000,000
Repurchase of senior notes	280,201,000	8,556,000
Premium on notes issued																												500,000
Principal and interest with a balloon payment																													$ 4,000,000
Amortization Period				At maturity			At maturity		At maturity			At maturity		At maturity				Payable in monthly installments of principal and interest based on a 20-year amortization with the final payment due at maturity.	Payable in monthly installments of principal and interest based on a 27-year amortization with the final payment due at maturity.	Payable in monthly installments of principal and interest based on a 10-year amortization with the final payment due at maturity.	Payable in monthly installments of principal and interest based on a 10-year amortization with the final payment due at maturity. The Company recorded a $2.7 million discount on this note upon acquisition which is included in the balance above.	Payable in monthly installments of principal and interest based on a 10-year amortization with the final payment due at maturity. The Company recorded a $2.1 million discount on this note upon acquisition which is included in the balance above.	Payable in monthly installments of interest only for 24 months and then installments of principal and interest based on an 11-year amortization with the final payment due at maturity. The Company recorded a $2.4 million discount on this note upon acquisition which is included in the balance above.	Payable in monthly installments of principal and interest based on a 9-year amortization with the final payment due at maturity. The unaccreted portion of the $0.2 million discount recorded on this note upon acquisition which is included in the balance above.	Payable in monthly installments of principal and interest based on a 12-year amortization with the final payment due at maturity. The unaccreted portion of the $1.0 million discount on this note upon acquisition which is included in the balance above.	Payable in monthly installments of principal and interest based on a 30-year amortization with a 7-year initial term (maturity 12/01/16) and the option to extend the initial term for two, one-year floating rate extension terms.	Payable in monthly installments of principal and interest based on a 15-year amortization with the final payment due at maturity. The Company acquired this mortgage note in an acquisition during the third quarter 2010.	Payable in monthly installments of principal and interest based on a 30-year amortization with the option to extend for three-years at a fixed rate of 6.75%. The unamortized portion of the $0.5 million premium recorded on this note upon acquisition which is included in the balance above.
Contractual interest rates, minimum																	5.00%
Contractual interest rates, maximum																	7.625%