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Schedule II - Valuation and Qualifying Accounts (Detail) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Allowance for Doubtful Accounts [Member]      
Valuation and Qualifying Accounts Disclosure [Line Items]      
Balance at beginning of period $ 2,815 $ 1,871 $ 1,943
Additions charged to costs and expenses 472 1,809 524
Deductions (432) (864) (414)
Other additions or deductions 55 (1) (182)
Balance at end of period 2,910 2,815 1,871
Reserve for Credit Memos [Member]      
Valuation and Qualifying Accounts Disclosure [Line Items]      
Balance at beginning of period 395 455 428
Additions charged to costs and expenses 693 (674) 437
Deductions (675)   (408)
Deductions   613  
Other additions or deductions 2 1 (2)
Balance at end of period 415 395 455
Slow-Moving and Obsolete Inventory Reserve [Member]      
Valuation and Qualifying Accounts Disclosure [Line Items]      
Balance at beginning of period 11,560 10,230 9,183
Additions charged to costs and expenses 998 2,825 2,477
Deductions (3,855) (1,408) (1,509)
Other additions or deductions 363 (87) 79
Balance at end of period 9,066 11,560 10,230
Accrued Product Warranty [Member]      
Valuation and Qualifying Accounts Disclosure [Line Items]      
Balance at beginning of period 1,058 714 892
Additions charged to costs and expenses 347 649 74
Deductions (399) (269) (158)
Other additions or deductions 70 (36) (94)
Balance at end of period 1,076 1,058 714
Foreign Net Operating Loss Tax Carryforwards [Member]      
Valuation and Qualifying Accounts Disclosure [Line Items]      
Balance at beginning of period 3,805 5,209 3,614
Additions charged to costs and expenses 490 346 2,105
Deductions (312) (1,175) (287)
Other additions or deductions (18) (575) (223)
Balance at end of period $ 3,965 $ 3,805 $ 5,209