Accrued Liabilities - Accrued Liabilities (Detail) (USD $)	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012	Dec. 31, 2011
Payables And Accruals [Abstract]
Accrued salaries and benefits	$ 1,836,857	$ 2,416,268
Accrued judgments and reserves	3,050,000	2,090,000
Accrued warranty expense	708,044	483,721	380,029	427,459
Accrued income and other taxes	115,832	295,595
Other accrued expenses	2,470,119	1,779,501
Accrued liabilities	$ 8,180,852	$ 7,065,085