Summary of Significant Accounting Policies - Narrative (Details)	12 Months Ended
Dec. 31, 2018 USD ($) customer	Dec. 31, 2017 USD ($) customer	Dec. 31, 2016 USD ($) customer
Schedule of Accounting Policies [Line Items]
Certificates of deposit	$ 0	$ 2,880,000
Investments held to maturity	0	6,077,000
Research and development costs	13,500,000	13,000,000	$ 12,000,000
Advertising expense	800,000	1,700,000	1,400,000
Payments to representatives	$ 47,800,000	51,800,000	55,000,000
Extended product warranties, minimum length	6 months
Extended product warranties, maximum length	10 years
Shipping and Handling
Schedule of Accounting Policies [Line Items]
Cost of sales	$ 12,600,000	$ 11,400,000	$ 10,300,000
Foreign Sales Revenue, Net
Schedule of Accounting Policies [Line Items]
Concentration risk, percentage	3.00%	4.00%	4.00%
Sales Revenue, Net
Schedule of Accounting Policies [Line Items]
Number of major customers \| customer	1	1	1
Accounting for More Than 5% of Accounts Receivable
Schedule of Accounting Policies [Line Items]
Concentration risk, percentage	5.00%	5.00%
Number of major customers	0	0

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Number of major customers.

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Amount charged to advertising expense for the period, which are expenses incurred with the objective of increasing revenue for a specified brand, product or product line.

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A savings certificate entitling the Entity (that is, bearer) to receive interest at an established maturity date, based upon a fixed interest rate. A certificate of deposit may be issued in any denomination. Certificates of deposit are generally issued by commercial banks and, therefore, insured by the FDIC (up to the prescribed limit). Certificates of deposit generally restrict holders from withdrawing funds on demand without the incurrence of penalties. Generally, only certificates of deposit with original maturities of three months or less qualify as cash equivalents. Original maturity means original maturity to the entity holding the investment. As a related example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three-years ago does not become a cash equivalent when its remaining maturity is three months.

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For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

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The aggregate costs related to goods produced and sold and services rendered by an entity during the reporting period. This excludes costs incurred during the reporting period related to financial services rendered and other revenue generating activities.

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Amount of investment in debt security measured at amortized cost (held-to-maturity).

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The aggregate costs incurred (1) in a planned search or critical investigation aimed at discovery of new knowledge with the hope that such knowledge will be useful in developing a new product or service, a new process or technique, or in bringing about a significant improvement to an existing product or process; or (2) to translate research findings or other knowledge into a plan or design for a new product or process or for a significant improvement to an existing product or process whether intended for sale or the entity's use, during the reporting period charged to research and development projects, including the costs of developing computer software up to the point in time of achieving technological feasibility, and costs allocated in accounting for a business combination to in-process projects deemed to have no alternative future use.

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Primarily represents commissions incurred in the period based upon the sale by commissioned employees or third parties of the entity's goods or services, and fees for sales assistance or product enhancements performed by third parties (such as a distributor or value added reseller).

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