Business Combinations - Additional Information (Detail) (USD $)	8 Months Ended	12 Months Ended				3 Months Ended		6 Months Ended	12 Months Ended		12 Months Ended
	Dec. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Apr. 29, 2011	Dec. 31, 2012 Scanners and CAD/CAM Services	Sep. 30, 2012 Scanners and CAD/CAM Services	Dec. 31, 2012 Scanners and CAD/CAM Services	Dec. 31, 2012 Scanners and CAD/CAM Services	Apr. 29, 2011 Scanners and CAD/CAM Services	Dec. 31, 2012 Clear Aligner	Apr. 29, 2011 Clear Aligner
Business Acquisition [Line Items]
Aggregate cash purchase price					$ 187,600,000
Transaction costs	6,400,000		6,400,000
Business acquisition, goodwill					135,349,000					77,300,000		58,000,000
Impairment of goodwill		36,591,000	0	0		11,900,000	24,700,000	36,591,000	36,591,000		0
Contributed revenues	28,000,000	43,500,000
Contributed gross profit	$ 6,500,000	$ 10,400,000