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Valuation and Qualifying Accounts (Detail) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Valuation and Qualifying Accounts Disclosure [Line Items]      
Balance at Beginning of Period $ 26,905 $ 28,032 $ 35,618
Charged to Costs and Expenses 62,050 50,724 43,875
Deductions (45,947) (51,851) (51,461)
Balance at End of Period 43,008 26,905 28,032
Uncollectible accounts      
Valuation and Qualifying Accounts Disclosure [Line Items]      
Balance at Beginning of Period 2,864 2,714 3,264
Charged to Costs and Expenses 11,803 303 (143)
Deductions (3,727) (153) (407)
Balance at End of Period 10,940 2,864 2,714
Reserve for potential product obsolescence      
Valuation and Qualifying Accounts Disclosure [Line Items]      
Balance at Beginning of Period 7,617 8,051 7,877
Charged to Costs and Expenses 7,593 (161) 1,511
Deductions (764) (273) (1,337)
Balance at End of Period 14,446 7,617 8,051
Reserve for sales returns and allowances      
Valuation and Qualifying Accounts Disclosure [Line Items]      
Balance at Beginning of Period 16,424 17,267 24,477
Charged to Costs and Expenses 42,654 50,582 42,507
Deductions (41,456) (51,425) (49,717)
Balance at End of Period $ 17,622 $ 16,424 $ 17,267