Notes and Bonds Payable - Future Maturities (Details) $ in Thousands		Dec. 31, 2015 USD ($) mortgage_note_payable	Dec. 31, 2014 USD ($)
Long Term Debt Maturities [Line Items]
Number of outstanding mortgage notes | mortgage_note_payable		16
Future contractual maturities of the Company's notes and bonds payable
Principal Maturities		$ 1,434,161
Net Accretion/Amortization	[1]	(2,667)
Notes and bonds payable		$ 1,431,494	$ 1,403,692
%		100.00%
2016 [Member]
Future contractual maturities of the Company's notes and bonds payable
Principal Maturities		$ 37,369
Net Accretion/Amortization	[1]	(24)
Notes and bonds payable		$ 37,345
%		2.60%
2017 [Member]
Future contractual maturities of the Company's notes and bonds payable
Principal Maturities		$ 209,701
Net Accretion/Amortization	[1]	(338)
Notes and bonds payable		$ 209,363
%		14.60%
2018 [Member]
Future contractual maturities of the Company's notes and bonds payable
Principal Maturities		$ 8,966
Net Accretion/Amortization	[1]	(399)
Notes and bonds payable		$ 8,567
%		0.60%
2019 [Member]
Future contractual maturities of the Company's notes and bonds payable
Principal Maturities		$ 220,950
Net Accretion/Amortization	[1]	(616)
Notes and bonds payable		$ 220,334
%		15.40%
2020 [Member]
Future contractual maturities of the Company's notes and bonds payable
Principal Maturities		$ 20,987
Net Accretion/Amortization	[1]	(783)
Notes and bonds payable		$ 20,204
%		1.40%
2021 and thereafter [Member]
Future contractual maturities of the Company's notes and bonds payable
Principal Maturities		$ 936,188
Net Accretion/Amortization	[1]	(507)
Notes and bonds payable		$ 935,681
%		65.40%

[1] Includes discount accretion and premium amortization related to the Company’s Senior Notes due 2021, Senior Notes due 2023, Senior Notes due 2025, and 16 mortgage notes payable.