Schedule II - Valuation and Qualifying Accounts (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020		Dec. 31, 2019	Dec. 31, 2018
Valuation and Qualifying Accounts [Roll Forward]
Balance at beginning of year	$ 5,212,000		$ 5,687,000	$ 4,967,000
Charged to costs and expenses	11,880,000		10,365,000	10,684,000
Other	0		0	0
Deductions	11,270,000		10,840,000	9,964,000
Balance at end of year	5,822,000		5,212,000	5,687,000
Allowance for Doubtful Accounts [Member]
Valuation and Qualifying Accounts [Roll Forward]
Balance at beginning of year	4,244,000		4,488,000	3,824,000
Charged to costs and expenses	392,000		(295,000)	325,000
Other	0		0	0
Deductions	230,000		(51,000)	(339,000)
Balance at end of year	4,406,000		4,244,000	4,488,000
Allowance for Discounts [Member]
Valuation and Qualifying Accounts [Roll Forward]
Balance at beginning of year	968,000		1,199,000	1,143,000
Charged to costs and expenses	11,488,000		10,660,000	10,359,000
Other	0		0	0
Deductions	11,040,000		10,891,000	10,303,000
Balance at end of year	1,416,000		968,000	1,199,000
Allowance for Sales Returns [Member]
Valuation and Qualifying Accounts [Roll Forward]
Balance at beginning of year	35,240,000		33,417,000	30,950,000
Charged to costs and expenses	135,448,000		136,777,000	132,390,000
Other	0	[1]	0	6,670,000	[1]
Deductions	129,706,000		134,954,000	136,593,000
Balance at end of year	$ 40,982,000		$ 35,240,000	$ 33,417,000

[1] The other addition to the allowance for sales returns represents the cumulative effect of the changes made to our consolidated balance sheet as of January 1, 2018 for the adoption of ASU 2014-09, Revenue from Contracts with Customers.