Notes and Bonds Payable (Details 6) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012		Dec. 31, 2011
Future contractual maturities of the Company's notes and bonds payable
Principal Maturities	$ 1,299,979
Net Accretion/Amortization	(6,935)	[1]
Notes and bonds payable	1,293,044	[2]	1,393,537	[2]
%	100.00%
2013 [Member]
Future contractual maturities of the Company's notes and bonds payable
Principal Maturities	20,258
Net Accretion/Amortization	(1,164)	[1]
Notes and bonds payable	19,094
%	1.50%
2014 [Member]
Future contractual maturities of the Company's notes and bonds payable
Principal Maturities	276,899
Net Accretion/Amortization	(1,234)	[1]
Notes and bonds payable	275,665
%	21.30%
2015 [Member]
Future contractual maturities of the Company's notes and bonds payable
Principal Maturities	50,357
Net Accretion/Amortization	(1,053)	[1]
Notes and bonds payable	49,304
%	3.80%
2016 [Member]
Future contractual maturities of the Company's notes and bonds payable
Principal Maturities	106,992
Net Accretion/Amortization	(798)	[1]
Notes and bonds payable	106,194
%	8.20%
2017 [Member]
Future contractual maturities of the Company's notes and bonds payable
Principal Maturities	412,132
Net Accretion/Amortization	(591)	[1]
Notes and bonds payable	411,541
%	31.80%
2018 and thereafter [Member]
Future contractual maturities of the Company's notes and bonds payable
Principal Maturities	433,341
Net Accretion/Amortization	(2,095)	[1]
Notes and bonds payable	$ 431,246
%	33.40%

[1] Includes discount accretion and premium amortization related to the Company’s Senior Notes due 2014, Senior Notes due 2017, Senior Notes due 2021, and fourteen mortgage notes payable.

[2] Level 3 - Fair value derived from valuation techniques in which one of more significant inputs or significant value drivers are unobservable.