Accrued Liabilities (Details) (USD $)	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Accrued liabilities
Accrued salaries and benefits	$ 2,416,268	$ 1,549,659
Accrued judgments and settlements	2,090,000	3,300,000
Accrued warranty expense	483,721	427,459	646,113	369,311
Accrued income and other taxes	295,595	272,300
Other accrued expenses	1,779,501	2,093,586
Accrued liabilities	$ 7,065,085	$ 7,643,004