Schedule II - Valuation and Qualifying Accounts (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Allowance for Doubtful Accounts [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of period		$ 175	$ 270	$ 360
Additions charged to costs and expenses		105	163	314
Deductions describe	[1],[2],[3]	120	258	404
Balance at end of period		160	175	270
Refund on Estimated Returns and Allowances [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of period		1,950
Additions charged to costs and expenses		18,748
Deductions describe	[1],[2],[3]	18,675
Balance at end of period		2,023	1,950
Refund on Cancelled Sales and Allowances [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of period		$ 1,950	2,072
Additions charged to costs and expenses			19,252
Deductions describe	[1],[2],[3]		19,374
Balance at end of period			1,950	2,072
Reserve for Cancelled Sales and Allowances [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of period			$ 1,464	1,772
Additions charged to costs and expenses				11,601
Deductions describe	[1],[2],[3]			11,909
Balance at end of period				$ 1,464

[1] Allowance for doubtful accounts: uncollectible accounts written off, net of recoveries.

[2] Refund on estimated returns and allowances: impact of sales cancelled after delivery plus amount of allowance given to customers.

[3] Reserve for cancelled sales and allowances: impact of sales cancelled after delivery plus amount of allowance given to customers.