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Business Combinations - Additional Information (Detail) (USD $)	12 Months Ended			3 Months Ended			6 Months Ended	0 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Dec. 31, 2012	Apr. 29, 2011	Apr. 30, 2013
Business Acquisition [Line Items]
Acquisition, net of cash acquired	$ 0	$ 7,652,000	$ 0
Goodwill	61,369,000us-gaap_Goodwill	61,623,000us-gaap_Goodwill	99,236,000us-gaap_Goodwill		99,236,000us-gaap_Goodwill		99,236,000us-gaap_Goodwill
Impairment of goodwill	0us-gaap_GoodwillImpairmentLoss	40,693,000us-gaap_GoodwillImpairmentLoss	36,591,000us-gaap_GoodwillImpairmentLoss
Gross profit	578,443,000us-gaap_GrossProfit	498,106,000us-gaap_GrossProfit	416,388,000us-gaap_GrossProfit
Scanners and CAD/CAM Services
Business Acquisition [Line Items]
Goodwill	0	0	40,693,000		40,693,000		40,693,000
Impairment of goodwill		40,693,000	36,600,000	40,700,000	11,900,000	24,700,000	36,600,000
Gross profit	15,554,000	13,271,000	10,418,000
Clear Aligner
Business Acquisition [Line Items]
Goodwill	61,369,000	61,623,000	58,543,000		58,543,000		58,543,000
Impairment of goodwill		0
Gross profit	562,889,000	484,835,000	405,970,000
Cadent [Member]
Business Acquisition [Line Items]
Acquisition, net of cash acquired								187,600,000
Goodwill								135,300,000
Cadent [Member] \| Scanners and CAD/CAM Services
Business Acquisition [Line Items]
Goodwill								77,300,000
Cadent [Member] \| Clear Aligner
Business Acquisition [Line Items]
Goodwill								58,000,000
ICA Holdings Pty Limited [Member]
Business Acquisition [Line Items]
Acquisition, net of cash acquired									8,600,000
Goodwill									3,600,000
Assets acquired									7,400,000
Liabilities assumed									$ 2,400,000