Income Taxes - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets:
State net operating loss carryforwards	$ 17,237	$ 14,956
Alternative minimum tax credit carryforward	0	13,477
Impairment losses	41,837	63,108
Prepaid income from land sales	3,734	5,461
Other	322	0
Total gross deferred tax assets	63,130	97,002
Valuation allowance	(4,993)	(5,135)
Total net deferred tax assets	58,137	91,867
Deferred tax liabilities:
Investment in real estate and property and equipment basis differences	525	647
Deferred gain on land sales and involuntary conversions	19,671	28,920
Installment sales	85,769	127,260
Pension Plan assets transferred to the 401(k) Plan	1,155	2,170
Other	0	1,716
Total gross deferred tax liabilities	107,120	160,713
Net deferred tax liabilities	$ (48,983)	$ (68,846)