Summary of Significant Accounting Policies, Balance Sheet (Details) - USD ($) $ in Thousands		Dec. 31, 2018	Dec. 31, 2017
Balance Sheet [Abstract]
Unreturned customer inventories	[1]	$ 20,484	$ 0
Prepaid expenses and other current assets		7,256	12,300
Accrued customer returns		57,433	35,916
Accrued core liability		31,263	11,899
Retained earnings		380,113	357,153
ASC 606 [Member]
Balance Sheet [Abstract]
Unreturned customer inventories			19,950
Accrued customer returns			42,586
Accrued core liability			26,368
Retained earnings			355,964
Adjustments Due to Adoption of ASU 2014-09 [Member] | ASC 606 [Member]
Balance Sheet [Abstract]
Unreturned customer inventories		20,484	19,950
Prepaid expenses and other current assets		(18)
Accrued customer returns		6,365	6,670
Accrued core liability		15,238	14,469
Retained earnings		(1,137)	$ (1,189)
Balance Without Adoption of ASU 2014-09 [Member] | ASC 606 [Member]
Balance Sheet [Abstract]
Unreturned customer inventories		0
Prepaid expenses and other current assets		7,274
Accrued customer returns		51,068
Accrued core liability		16,025
Retained earnings		$ 381,250

[1] The adoption of ASU 2014-09 using the modified retrospective method resulted in the recording of unreturned customer inventories commencing on January 1, 2018, see Note 1, "Summary of Significant Accounting Policies" for additional information.