Receivables - Receivables (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	$ 13,030	$ 8,957
Allowance for bad debts	(26)	(26)
Receivables, net	13,004	8,931
Receivables and accrued interest
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	6,958	1,505
Notes receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	$ 6,072	$ 7,452
Average interest rates	5.13%	4.94%