Schedule II - Valuation and Qualifying Accounts (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Allowance for Doubtful Accounts [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at beginning of period	$ 2,910	$ 2,815	$ 1,871
Additions charged to costs and expenses	449	472	1,809
Deductions	(529)	(432)	(864)
Other additions or deductions	(178)	55	(1)
Balance at end of period	2,652	2,910	2,815
Reserve for Credit Memos [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at beginning of period	415	395	455
Additions charged to costs and expenses	802	693	(674)
Deductions	(688)	(675)
Deductions			613
Other additions or deductions	(3)	2	1
Balance at end of period	526	415	395
Slow-Moving and Obsolete Inventory Reserve [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at beginning of period	9,066	11,560	10,230
Additions charged to costs and expenses	1,341	998	2,825
Deductions	(1,658)	(3,855)	(1,408)
Other additions or deductions	(287)	363	(87)
Balance at end of period	8,462	9,066	11,560
Accrued Product Warranty [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at beginning of period	1,076	1,058	714
Additions charged to costs and expenses	97	347	649
Deductions	(133)	(399)	(269)
Other additions or deductions	(112)	70	(36)
Balance at end of period	928	1,076	1,058
Deferred Tax Asset Valuation Allowance [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at beginning of period	3,965	3,805	5,209
Additions charged to costs and expenses	568	490	346
Deductions	(761)	(312)	(1,175)
Other additions or deductions	(277)	(18)	(575)
Balance at end of period	$ 3,495	$ 3,965	$ 3,805