Fair Value Disclosures, Non-recurring (Detail) - Fair Value, Measurements, Nonrecurring - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Real Estate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, nonrecurring	$ 0	$ 180,247
Real Estate [Member] | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, nonrecurring	0	0
Real Estate [Member] | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, nonrecurring	0	180,247
Real Estate [Member] | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, nonrecurring	0	0
Water Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, nonrecurring	0	1,987
Water Assets [Member] | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, nonrecurring	0	0
Water Assets [Member] | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, nonrecurring	0	0
Water Assets [Member] | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure, nonrecurring	$ 0	$ 1,987