Goodwill and Intangible Assets - Change in the Carrying Value of Goodwill (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended							3 Months Ended		6 Months Ended	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 Clear Aligner		Dec. 31, 2011 Clear Aligner	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		Dec. 31, 2011 Scanners and CAD/CAM Services
Goodwill [Roll Forward]
Balance, Beginning Balance	$ 135,383		$ 478		$ 58,445		$ 478				$ 76,938		$ 0
Adjustment to goodwill	444	[1]	134,905		98	[1]	57,967				346	[1]	76,938
Impairment of goodwill	(36,591)		0	0	0			(11,900)	(24,700)	(36,591)	(36,591)
Balance, Ending Balance	$ 99,236		$ 135,383	$ 478	$ 58,543		$ 58,445	$ 40,693		$ 40,693	$ 40,693		$ 76,938

[1] Pursuant to the accounting guidance for business combinations, we recorded goodwill adjustments for the effect on goodwill of changes to net assets acquired related our acquisition of Cadent during the measurement period (up to one year from April 29, 2011, the date of our acquisition of Cadent). Goodwill adjustments were not significant to our previously reported operating results or financial position.