Investments and Fair Value Measurements Short-Term and Long-Term Marketable Securities (Details) - Fair Value, Measurements, Recurring - Short-term Investments $ in Thousands	Dec. 31, 2019 USD ($)
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Amortized Cost Basis, Total	$ 318,008
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	224
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	(30)
Available-for-sale Securities, Total	318,202
Corporate Bonds
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Amortized Cost Basis, Total	210,891
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	142
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	(27)
Available-for-sale Securities, Total	211,006
Commercial paper
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Amortized Cost Basis, Total	14,426
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	0
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	0
Available-for-sale Securities, Total	14,426
U.S. government treasury bonds
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Amortized Cost Basis, Total	70,587
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	65
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	(2)
Available-for-sale Securities, Total	70,650
U.S. government agency bonds
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Amortized Cost Basis, Total	22,085
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	17
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	(1)
Available-for-sale Securities, Total	22,101
Certificates of deposit
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Amortized Cost Basis, Total	19
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	0
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	0
Available-for-sale Securities, Total	$ 19

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

No definition available.

Name:	us-gaap_AvailableForSaleSecurities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

+ Details

Name:	us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

No definition available.

+ Details

Name:	us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

+ References

No definition available.

+ Details

Name:	us-gaap_AvailableForSaleSecuritiesAmortizedCost
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_FairValueByMeasurementFrequencyAxis=us-gaap_FairValueMeasurementsRecurringMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_ShortTermInvestmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=algn_CorporateBondsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_CommercialPaperMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_USTreasuryAndGovernmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_AgencySecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_CertificatesOfDepositMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: