Valuation and Qualifying Accounts (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Allowance for doubtful accounts
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Year	$ 977	$ 969	$ 881
Charged to Income	321	136	53
Deductions from Reserves	(179)	(128)	(30)
Other Adjustments	0	0	65
Balance at End of Year	1,119	977	969
Rebates and allowances
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Year	2,860	2,297	2,303
Charged to Income	13,202	9,568	7,255
Deductions from Reserves	(11,047)	(8,351)	(6,809)
Other Adjustments	(361)	(654)	(452)
Balance at End of Year	$ 4,654	$ 2,860	$ 2,297