Notes and Bonds Payable (Details 7) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Future contractual maturities of the Company's notes and bonds payable
Principal Maturities	$ 1,402,114
Net Accretion/Amortization	(8,577)
Notes and Bonds Payable	1,393,537	1,407,855
%	100.00%
2012 [Member]
Future contractual maturities of the Company's notes and bonds payable
Principal Maturities	4,948
Net Accretion/Amortization	(1,019)
Notes and Bonds Payable	3,929
%	0.30%
2013 [Member]
Future contractual maturities of the Company's notes and bonds payable
Principal Maturities	19,781
Net Accretion/Amortization	(1,263)
Notes and Bonds Payable	18,518
%	1.30%
2014 [Member]
Future contractual maturities of the Company's notes and bonds payable
Principal Maturities	276,349
Net Accretion/Amortization	(1,404)
Notes and Bonds Payable	274,945
%	19.70%
2015 [Member]
Future contractual maturities of the Company's notes and bonds payable
Principal Maturities	261,775
Net Accretion/Amortization	(1,215)
Notes and Bonds Payable	260,560
%	18.70%
2016 [Member]
Future contractual maturities of the Company's notes and bonds payable
Principal Maturities	106,376
Net Accretion/Amortization	(907)
Notes and Bonds Payable	105,469
%	7.60%
2017 and thereafter [Member]
Future contractual maturities of the Company's notes and bonds payable
Principal Maturities	732,885
Net Accretion/Amortization	(2,769)
Notes and Bonds Payable	$ 730,116
%	52.40%