Schedule II - Valuation and Qualifying Accounts (Detail) - Allowance for Doubtful Accounts - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Movement in Valuation Allowances and Reserves
Balance at Beginning of Period	$ 729	$ 443	$ 322
Charged to Costs and Expenses	1,189	592	205
Charged to Other Accounts	0	0	0
Deductions	(36)	(306)	(84)
Balance at End of Period	$ 1,882	$ 729	$ 443