Fair Value - Carrying Value of Assets (Detail) - Non-recurring - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Real Estate
Non-Financial Assets and Liabilities:
Assets, fair value disclosure, nonrecurring	$ 180,247	$ 0
Real Estate | Level 1
Non-Financial Assets and Liabilities:
Assets, fair value disclosure, nonrecurring	0	0
Real Estate | Level 2
Non-Financial Assets and Liabilities:
Assets, fair value disclosure, nonrecurring	180,247	0
Real Estate | Level 3
Non-Financial Assets and Liabilities:
Assets, fair value disclosure, nonrecurring	0	0
Central Texas water assets
Non-Financial Assets and Liabilities:
Assets, fair value disclosure, nonrecurring	1,987	0
Central Texas water assets | Level 1
Non-Financial Assets and Liabilities:
Assets, fair value disclosure, nonrecurring	0	0
Central Texas water assets | Level 2
Non-Financial Assets and Liabilities:
Assets, fair value disclosure, nonrecurring	0	0
Central Texas water assets | Level 3
Non-Financial Assets and Liabilities:
Assets, fair value disclosure, nonrecurring	$ 1,987	$ 0