Accrued Liabilities - Accrued Liabilities (Detail) (USD $)	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2012	Dec. 31, 2011
Payables And Accruals [Abstract]
Accrued salaries and benefits	$ 2,350,891	$ 2,416,268
Accrued judgments and reserves	1,850,000	2,090,000
Accrued warranty expense	694,394	483,721	360,107	427,459
Accrued income and other taxes	104,518	295,595
Other accrued expenses	2,425,801	1,779,501
Accrued liabilities	$ 7,425,604	$ 7,065,085