Long Term Water Assets - Tangible Water Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Long Lived Assets Held For Sale [Line Items]
Total water held for future use at cost	$ 18,571	$ 13,854
Banked water and water for future delivery
Long Lived Assets Held For Sale [Line Items]
Total water held for future use at cost	5,220	4,779
Transferable water
Long Lived Assets Held For Sale [Line Items]
Total water held for future use at cost	$ 13,351	$ 9,075