Investments and Fair Value Measurements Additional Information (Details)	9 Months Ended	12 Months Ended
Sep. 30, 2018	Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract]
Original maturity of highly liquid investments included in cash and cash equivalents	40 months
Weighted average maturity	3 months	6 months

Marketable Securities, Weighted Average Remaining Maturity

No definition available.

Name:	algn_MarketableSecuritiesWeightedAverageRemainingMaturity
Namespace Prefix:	algn_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration