Fair Value - Additional Information (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) community_development_project	Dec. 31, 2016 USD ($) community_development_project multifamily_site	Dec. 31, 2015 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Asset impairments	$ 47,172	$ 60,939	$ 108,184
Real Estate Impairment Charges
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Asset impairments	$ 3,420	$ 56,453
Community Development Project
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Number of properties impaired | community_development_project	1	6
Multifamily Site
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Number of properties impaired | multifamily_site		2
Oil and Gas Properties
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impairment of assets to be disposed of		$ 612
Disposal Group, Disposed of by Sale, Not Discontinued Operations | Community Development Project
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Number of properties impaired | community_development_project		4
Disposal Group, Disposed of by Sale, Not Discontinued Operations | Multifamily Site
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Number of properties impaired | multifamily_site		1
The Mineral Companies | Disposal Group, Disposed of by Sale, Not Discontinued Operations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Asset impairments	$ 37,900
Water Resources Company | Georgia and Texas
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Asset impairments	5,852
Water Resources Company | Georgia
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Asset impairments	420
Equity Method Investments | Cost of Real Estate Sales
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Asset impairments	$ 3,000