Valuation and Qualifying Accounts (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Allowance for Doubtful Accounts
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	$ 495	$ 359	$ 252
Additions Charged to Costs and Expenses	334	233	235
Deductions/(Recoveries)	(39)	97	128
Balance at End of Period	868	495	359
Valuation Allowance of Deferred Tax Assets
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	6,607	7,477	6,882
Additions Charged to Costs and Expenses	2,406	(870)	595
Deductions/(Recoveries)	0	0	0
Balance at End of Period	$ 9,013	$ 6,607	$ 7,477