Derivatives designated as hedging instruments - Effect of foreign currency exchange and interest rate swap contracts (Details) - USD ($) $ in Thousands	3 Months Ended
Jun. 30, 2020	Jun. 30, 2019
Designated As Hedging Instrument \| Cash flow hedges. \| Revenue
Derivative Financial Instruments
Amount of Gain or (Loss) Reclassified from AOCI into Income (loss)		$ (18)
Designated As Hedging Instrument \| Cash flow hedges. \| Costs of revenue
Derivative Financial Instruments
Amount of Gain or (Loss) Reclassified from AOCI into Income (loss)	$ (613)	405
Designated As Hedging Instrument \| Cash flow hedges. \| Operating Expense
Derivative Financial Instruments
Amount of Gain or (Loss) Reclassified from AOCI into Income (loss)	(240)	200
Designated As Hedging Instrument \| Cash flow hedges. \| Interest expenses
Derivative Financial Instruments
Amount of Gain or (Loss) Reclassified from AOCI into Income (loss)	(710)	208
Designated As Hedging Instrument \| Cash flow hedges. \| Foreign Exchange Contract
Derivative Financial Instruments
Amount of Gain or (Loss) Recognized in AOCI on Derivatives	1,964	2,633
Designated As Hedging Instrument \| Cash flow hedges. \| Interest rate swaps
Derivative Financial Instruments
Amount of Gain or (Loss) Recognized in AOCI on Derivatives	(735)	(3,045)
Nondesignated \| Foreign Exchange Contract \| Revenue
Derivative Financial Instruments
Amount of Gain or (Loss) Recognized in Income (loss) on Derivatives	(129)	355
Nondesignated \| Foreign Exchange Contract \| Costs of revenue
Derivative Financial Instruments
Amount of Gain or (Loss) Recognized in Income (loss) on Derivatives	145	(226)
Nondesignated \| Foreign Exchange Contract \| Selling General And Administrative Expenses
Derivative Financial Instruments
Amount of Gain or (Loss) Recognized in Income (loss) on Derivatives	$ 14	$ (20)

Amount of increase (decrease) in the fair value of derivatives recognized in the income statement.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4A
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5618551-113959

+ Details

Name:	us-gaap_DerivativeGainLossOnDerivativeNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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_DerivativeInstrumentsGainLossLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount before tax and reclassification adjustments of other comprehensive income (loss).

+ References

+ Details

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

- Definition

Amount before tax of reclassification adjustments of other comprehensive income (loss).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 14A
-URI http://asc.fasb.org/extlink&oid=118930883&loc=SL7669686-108580

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 17B
-URI http://asc.fasb.org/extlink&oid=118930883&loc=SL34724394-108580

+ Details

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

- Details

Name:	us-gaap_HedgingDesignationAxis=us-gaap_DesignatedAsHedgingInstrumentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis=us-gaap_CashFlowHedgingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_IncomeStatementLocationAxis=us-gaap_SalesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_IncomeStatementLocationAxis=us-gaap_CostOfSalesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_IncomeStatementLocationAxis=us-gaap_OperatingExpenseMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_IncomeStatementLocationAxis=us-gaap_InterestExpenseMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_ForeignExchangeContractMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_InterestRateSwapMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_HedgingDesignationAxis=us-gaap_NotDesignatedAsHedgingInstrumentEconomicHedgeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_IncomeStatementLocationAxis=us-gaap_SellingGeneralAndAdministrativeExpensesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: