Schedule II - Valuation and Qualifying Accounts (Detail) - Allowance for Doubtful Accounts [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	$ 88	$ 120	$ 120
Additions (Recovery) to Bad Debt Expense	(17)	57	0
Charged to Other Accounts	0	0	0
Deductions	0	(89)	0
Balance at End of Period	$ 71	$ 88	$ 120