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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-Publisher FASB
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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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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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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
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Period Type:	duration

- Definition

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

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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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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

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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

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Data Type:	xbrli:stringItemType
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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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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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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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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

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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

Name:	us-gaap_DebtInstrumentAxis=jcom_A6SeniorNotesMember
Namespace Prefix:
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Period Type:

- Details

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Balance Type:
Period Type:

- Details

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Namespace Prefix:
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Period Type:

- Details

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Namespace Prefix:
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Debt (Details) $ / shares in Units, $ in Thousands			3 Months Ended		6 Months Ended
Debt (Details) $ / shares in Units, $ in Thousands	Jun. 27, 2017 USD ($)	Jun. 10, 2014 USD ($)	Jun. 30, 2020 USD ($) $ / shares	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($) $ / shares	Jun. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)	Nov. 15, 2019 USD ($)
Debt Instrument [Line Items]
Debt Instrument, Face Amount			$ 1,602,414		$ 1,602,414		$ 1,602,500
Debt Instrument, Unamortized Discount			127,381		127,381		139,981
Long-term Debt, Fair Value			1,600,000		1,600,000		1,800,000
Unamortized Debt Issuance Expense			(12,577)		(12,577)		(14,058)
Debt Issuance Costs, Line of Credit Arrangements, Gross			400		400
Debt Issuance Costs, Line of Credit Arrangements, Net			300		300
Debt, Long-term and Short-term, Combined Amount			1,462,456		1,462,456		1,448,461
Current maturities of long-term debt			391,092		391,092		385,532
Total long-term debt, less current portion			1,071,364		1,071,364		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		$ 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			661,400		$ 661,400		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		$ 402,500	$ 402,414		$ 402,414		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		$ 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
Long-term Debt, Fair Value			$ 446,000		$ 446,000		583,600
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		550,000
Debt Instrument, Maturity Date					Nov. 01, 2026
Common Stock, Conversion Features					7.9864
Debt Instrument, Convertible, Conversion Price \| $ / shares			$ 125.21		$ 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 3 months 18 days
Long-term Debt, Fair Value			$ 465,900		$ 465,900		$ 559,600
Proceeds from Debt, Net of Issuance Costs					537,100
Deferred Finance Cost Gross								10,100
Debt Issuance Costs, Gross			12,900		12,900
Unamortized Debt Issuance Expense			(9,500)		(9,500)
Line of Credit [Member]
Debt Instrument [Line Items]
Interest Expense			$ 0	$ 1,200	$ 0	$ 1,200
Equity Component [Member]
Debt Instrument [Line Items]
Deferred Finance Cost Gross								$ 2,800