Deferred Finance Cost, Gross

No definition available.

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Namespace Prefix:	jcom_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The carrying amount of the equity component of convertible debt which may be settled in cash upon conversion.

+ References

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

- Definition

The price per share of the conversion feature embedded in the debt instrument.

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Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	instant

- Definition

Ratio applied to the conversion of debt instrument into equity with equity shares divided by debt principal amount.

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Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	duration

- Definition

Remaining amortization period for discount on the liability component of convertible debt which may be settled in cash upon conversion, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Face (par) amount of debt instrument at time of issuance.

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

- Definition

Description of the frequency of periodic payments (monthly, quarterly, annual).

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

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

+ Details

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Date the debt instrument was issued, in CCYY-MM-DD format.

+ References

+ Details

Name:	us-gaap_DebtInstrumentIssuanceDate1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
Balance Type:	na
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_DebtInstrumentLineItems
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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format.

+ References

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Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount, after accumulated amortization, of debt discount.

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

- Definition

Amount, before accumulated amortization, of debt issuance costs related to line of credit arrangements. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount, after accumulated amortization, of debt issuance costs related to line of credit arrangements. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

+ References

+ Details

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

- Definition

Represents the aggregate of total long-term debt, including current maturities and short-term debt.

+ References

No definition available.

+ Details

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

- Definition

Amount, before accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

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

- Definition

Amount of the cost of borrowed funds accounted for as interest expense.

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+ Details

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

- Definition

Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt, classified as current. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

+ Details

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

- Definition

The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

+ References

No definition available.

+ Details

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

- Definition

Amount after unamortized (discount) premium and debt issuance costs of long-term debt classified as noncurrent and excluding amounts to be repaid within one year or the normal operating cycle, if longer. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

+ Details

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

- Definition

The cash inflow from additional borrowings, net of cash paid to third parties in connection with debt origination.

+ References

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-SubTopic 10
-Section 45
-Paragraph 14
-Subparagraph (b)
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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The remaining balance of debt issuance expenses that were capitalized and are being amortized against income over the lives of the respective bond issues. This does not include the amounts capitalized as part of the cost of the utility plant or asset.

+ References

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=jcom_A325ConvertibleDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=us-gaap_LineOfCreditMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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Namespace Prefix:
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- Details

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Period Type:

Long Term Debt (Details) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2020 USD ($) $ / shares	Mar. 31, 2019 USD ($)	Dec. 31, 2019 USD ($)	Nov. 15, 2019 USD ($)	Jun. 10, 2014 USD ($)
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 1,602,499		$ 1,602,500
Debt Instrument, Unamortized Discount	133,726		139,981
Long-term Debt, Fair Value	1,600,000		1,800,000
Unamortized Debt Issuance Expense	(13,327)		(14,058)
Debt Issuance Costs, Line of Credit Arrangements, Gross	400
Debt Issuance Costs, Line of Credit Arrangements, Net	300
Debt, Long-term and Short-term, Combined Amount	1,455,446		1,448,461
Current maturities of long-term debt	0		385,532
Total long-term debt, less current portion	$ 1,455,446		1,062,929
6% Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Issuance Date	Jun. 27, 2017
Debt Instrument, Face Amount	$ 650,000		650,000
Debt Instrument, Interest Rate, Stated Percentage	6.00%
Debt Instrument, Frequency of Periodic Payment	semi-annually
Debt Instrument, Maturity Date	Jul. 15, 2025
Long-term Debt, Fair Value	$ 653,300		689,800
Proceeds from Debt, Net of Issuance Costs	$ 636,500
3.25% Convertible Debt Securities [Member]
Debt Instrument [Line Items]
Debt Instrument, Issuance Date	Jun. 10, 2014
Debt Instrument, Face Amount	$ 402,499		402,500
Debt Instrument, Interest Rate, Stated Percentage	3.25%
Debt Instrument, Frequency of Periodic Payment	semiannually
Debt Instrument, Maturity Date	Jun. 15, 2029
Common Stock, Conversion Features	14.7632
Debt Instrument, Convertible, Conversion Price \| $ / shares	$ 67.74
Debt Instrument, Unamortized Discount					$ 59,000
Debt Instrument, Convertible, Carrying Amount of Equity Component					$ 37,700
Debt Instrument, Convertible, Remaining Discount Amortization Period	1 year 2 months 12 days
Long-term Debt, Fair Value	$ 487,800		583,600
Line of Credit [Member]
Debt Instrument [Line Items]
Interest Expense	$ 0	$ 0
1.75% Convertible Debt Securities [Member]
Debt Instrument [Line Items]
Debt Instrument, Issuance Date	Nov. 15, 2019
Debt Instrument, Face Amount	$ 550,000		550,000
Debt Instrument, Maturity Date	Nov. 01, 2026
Common Stock, Conversion Features	7.9864
Debt Instrument, Convertible, Conversion Price \| $ / shares	$ 125.21
Debt Instrument, Unamortized Discount				$ 118,900
Debt Instrument, Convertible, Carrying Amount of Equity Component				88,100
Debt Instrument, Convertible, Remaining Discount Amortization Period	6 years 7 months 6 days
Long-term Debt, Fair Value	$ 507,300		$ 559,600
Proceeds from Debt, Net of Issuance Costs	537,100
Deferred Finance Cost Gross				10,100
Debt Issuance Costs, Gross	12,900
Unamortized Debt Issuance Expense	$ (9,700)
Equity Component [Member]
Debt Instrument [Line Items]
Deferred Finance Cost Gross				$ 2,800