Summary of Significant Accounting Policies - Narrative (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Schedule of Accounting Policies [Line Items]
Investments in certificates of deposit	$ 11,400,000	$ 10,700,000
Certificates of deposit interest rate, lower range	0.20%
Certificates of deposit interest rate, upper range	0.60%
Investments held to maturity	15,987,000	27,021,000
Research and development costs	6,300,000	5,200,000	3,600,000
Advertising expense	1,000,000	900,000	900,000
Shipping and handling fees	8,500,000	7,900,000	8,600,000
Payments to representatives	$ 59,700,000	$ 63,000,000	$ 57,100,000
Extended product warranties, minimum length	6 months
Extended product warranties, maximum length	10 years
Foreign Sales [Member]
Schedule of Accounting Policies [Line Items]
Concentration risk, percentage	6.00%	5.00%	5.00%
Accounting for More Than 10% of Sales
Schedule of Accounting Policies [Line Items]
Number of major customers	0	0	0
Accounting for More Than 5% of Accounts Receivable
Schedule of Accounting Policies [Line Items]
Number of major customers		1
Concentration risk, percentage	5.00%	5.00%
Minimum
Schedule of Accounting Policies [Line Items]
Certificates of deposit maturity dates	1 month
Investments maturity date	1 month
Maximum
Schedule of Accounting Policies [Line Items]
Certificates of deposit maturity dates	19 months
Investments maturity date	19 months