Real Estate - Narrative (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020 USD ($)	Sep. 30, 2020 USD ($)	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2020 USD ($) a $ / a	Dec. 31, 2019 USD ($) a $ / a	Dec. 31, 2018 USD ($) a $ / a
Real Estate Properties [Line Items]
Revenue	$ 74,304	$ 74,383	$ 57,273	$ 96,594	$ 113,332	$ 98,530	$ 87,310	$ 191,324	$ 302,554	$ 490,496	$ 300,220
Texas
Real Estate Properties [Line Items]
Area of real estate property, sold (in acres) | a									22,160	21,986	171
Acres of land exchanged from trust (in acres) | a										5,620
Acres of land received from exchange (in acres) | a										5,545
Additions (acres) | a									756	21,671	14,650
Land sales
Real Estate Properties [Line Items]
Revenue									$ 17,383	$ 135,020	$ 4,367
Land sales | Texas
Real Estate Properties [Line Items]
Proceeds from sale of real estate									$ 16,000	$ 113,000	$ 4,400
Average sales price (in USD per acre) | $ / a									721	5,141	25,464
Revenue									$ 1,400	$ 22,000
Land acquisitions | Texas
Real Estate Properties [Line Items]
Additions									$ 3,900	$ 74,400	$ 9,400
Average purchase price (in USD per acre) | $ / a									5,134	3,434	640