Revenue from Contracts with Customers - Changes in Accrued Revenue and Allowance for Doubtful Accounts (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2018
Allowance for Doubtful Accounts Receivable [Roll Forward]
Balance, December 31, 2017	$ 160
Charges	(19)
Write-offs	(2)
Balance, March 31, 2018	139
Accrued Revenue		$ 12,232
Less: Allowance for doubtful accounts	160	139
Accrued revenue, net		12,093
Real estate segment
Allowance for Doubtful Accounts Receivable [Roll Forward]
Balance, December 31, 2017	109
Charges	(19)
Write-offs	(22)
Balance, March 31, 2018	68
Accrued Revenue		12,093
Less: Allowance for doubtful accounts	109	68
Accrued revenue, net		12,025
Other segment
Allowance for Doubtful Accounts Receivable [Roll Forward]
Balance, December 31, 2017	51
Charges	0
Write-offs	20
Balance, March 31, 2018	71
Accrued Revenue		139
Less: Allowance for doubtful accounts	$ 51	71
Accrued revenue, net		$ 68