Income Taxes - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Deferred tax assets:
State net operating loss carryforwards	$ 13,355	$ 14,316
Impairment losses	33,660	36,751
Prepaid income from land sales	3,812	3,180
Capitalized costs	2,851	2,468
Reserves and accruals	1,586	1,672
Unrealized losses on investments	3,403	2,282
Other	765	765
Total gross deferred tax assets	59,432	61,434
Deferred tax liabilities:
Investment in real estate and property and equipment basis differences	5,929	4,000
Deferred gain on land sales and involuntary conversions	29,101	24,956
Installment sales	83,337	83,275
Pension Plan assets transferred to the 401(k) Plan	287	580
Other	1,693	1,431
Total gross deferred tax liabilities	120,347	114,242
Net deferred tax liabilities	$ (60,915)	$ (52,808)