Defined Contribution Plan, Employer Discretionary Contribution, Maximum Percentage

No definition available.

Name:	bsy_DefinedContributionPlanEmployerDiscretionaryContributionMaximumPercentage
Namespace Prefix:	bsy_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of contributions made by employer into fund established for purposes of making future disbursement to individual in accordance with deferred compensation arrangement.

+ References

No definition available.

+ Details

Name:	us-gaap_DeferredCompensationArrangementWithIndividualContributionsByEmployer
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Aggregate carrying value as of the balance sheet date of the liabilities for all deferred compensation arrangements. Represents currently earned compensation under compensation arrangements that is not actually paid until a later date.

+ References

No definition available.

+ Details

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

- Definition

Amount of cost for defined contribution plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 70
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=49170846&loc=d3e28014-114942

+ Details

Name:	us-gaap_DefinedContributionPlanCostRecognized
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

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

- Definition

Amount of paid and unpaid common stock dividends declared with the form of settlement in payment-in-kind (PIK).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-URI http://asc.fasb.org/extlink&oid=120397183&loc=d3e187085-122770

+ Details

Name:	us-gaap_DividendsCommonStockPaidinkind
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Percentage of vesting of award under share-based payment arrangement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901

+ Details

Name:	us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_DeferredCompensationArrangementWithIndividualPostretirementBenefitsByTypeOfDeferredCompensationAxis=us-gaap_DeferredCompensationArrangementWithIndividualByTypeOfCompensationPensionAndOtherPostretirementBenefitsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RetirementPlanSponsorLocationAxis=us-gaap_ForeignPlanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RetirementPlanTaxStatusAxis=us-gaap_QualifiedPlanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RetirementPlanSponsorLocationAxis=country_US
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RetirementPlanTaxStatusAxis=us-gaap_NonqualifiedPlanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VestingAxis=us-gaap_ShareBasedCompensationAwardTrancheOneMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardDateAxis=bsy_PriorToJanuary2016AwardsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardDateAxis=bsy_AfterJanuary2016AwardsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VestingAxis=us-gaap_ShareBasedCompensationAwardTrancheTwoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VestingAxis=us-gaap_ShareBasedCompensationAwardTrancheThreeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VestingAxis=bsy_ShareBasedPaymentArrangementTrancheFourMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VestingAxis=bsy_ShareBasedPaymentArrangementTrancheFiveMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Retirement Plans - Narrative (Details) - USD ($)		9 Months Ended		12 Months Ended
Retirement Plans - Narrative (Details) - USD ($)	Aug. 28, 2020	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018
Deferred Compensation Arrangement with Individual, by Type of Compensation, Pension and Other Postretirement Benefits
Defined Contribution Plan Disclosure [Line Items]
Deferred compensation liability, current and noncurrent		$ 2,300,000		$ 2,544,000	$ 2,275,000
Foreign Plan
Defined Contribution Plan Disclosure [Line Items]
Employer contributions				$ 8,070,000	7,613,000
Qualified Plan
Defined Contribution Plan Disclosure [Line Items]
Employer discretionary contribution, percent of qualified cash compensation (up to)		5.00%		5.00%
Qualified Plan \| United States
Defined Contribution Plan Disclosure [Line Items]
Employer contributions		$ 2,600,000	$ 2,423,000	$ 3,311,000	$ 3,337,000
Qualified Plan \| Foreign Plan
Defined Contribution Plan Disclosure [Line Items]
Employer contributions		5,566,000	5,956,000
Nonqualified Plan
Defined Contribution Plan Disclosure [Line Items]
Contributions by employer		$ 0	$ 0
Dividends, common stock, paid-in-kind	$ 41,948,000
Share-based Payment Arrangement, Tranche One \| Nonqualified Plan \| Deferred Compensation Arrangement with Individual, by Type of Compensation, Pension and Other Postretirement Benefits \| Prior to January 2016 Awards [Member]
Defined Contribution Plan Disclosure [Line Items]
Vesting percentage		20.00%		20.00%
Share-based Payment Arrangement, Tranche One \| Nonqualified Plan \| Deferred Compensation Arrangement with Individual, by Type of Compensation, Pension and Other Postretirement Benefits \| After January 2016 Awards [Member]
Defined Contribution Plan Disclosure [Line Items]
Vesting percentage		100.00%		100.00%
Share-based Payment Arrangement, Tranche Two \| Nonqualified Plan \| Deferred Compensation Arrangement with Individual, by Type of Compensation, Pension and Other Postretirement Benefits \| Prior to January 2016 Awards [Member]
Defined Contribution Plan Disclosure [Line Items]
Vesting percentage		20.00%
Share-based Payment Arrangement, Tranche Three \| Nonqualified Plan \| Deferred Compensation Arrangement with Individual, by Type of Compensation, Pension and Other Postretirement Benefits \| Prior to January 2016 Awards [Member]
Defined Contribution Plan Disclosure [Line Items]
Vesting percentage		20.00%		20.00%
Share-Based Payment Arrangement, Tranche Four \| Nonqualified Plan \| Deferred Compensation Arrangement with Individual, by Type of Compensation, Pension and Other Postretirement Benefits \| Prior to January 2016 Awards [Member]
Defined Contribution Plan Disclosure [Line Items]
Vesting percentage		20.00%
Share-Based Payment Arrangement, Tranche Five \| Nonqualified Plan \| Deferred Compensation Arrangement with Individual, by Type of Compensation, Pension and Other Postretirement Benefits \| Prior to January 2016 Awards [Member]
Defined Contribution Plan Disclosure [Line Items]
Vesting percentage		20.00%		20.00%