Amortization expense (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Expected Amortization Expense [Line Items]
Amortization expense	$ 572,000	$ 456,000	$ 291,000
Customer lists
Expected Amortization Expense [Line Items]
Amortization expense	78,000	78,000	50,000
Trademarks, patents and copyrights
Expected Amortization Expense [Line Items]
Amortization expense	$ 494,000	$ 378,000	$ 241,000