The amount available for debt and equity issuance under Shelf Registration.

No definition available.

Name:	gbl_AmountAvailableForDebtAndEquityIssuanceUnderShelfRegistration
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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The number of shares issuable in exchange for the original debt being converted in a noncash (or part noncash) transaction.

+ References

No definition available.

+ Details

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Balance Type:	na
Period Type:	instant

- Definition

Term of the interest rate that fluctuates over time as a result of an underlying benchmark interest rate or index.

+ References

No definition available.

+ Details

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- Definition

The cash outflow for the extinguishment of long-term borrowing before its maturity.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The maximum amount of debt and equity to be issued under the Shelf Registration.

+ References

No definition available.

+ Details

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

- Definition

Period of interest included in Initial Deposit, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

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Balance Type:	na
Period Type:	duration

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

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Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 5
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=6928298&loc=SL6031898-161870

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Balance Type:	na
Period Type:	instant

- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=64930739&loc=d3e28878-108400

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-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28551-108399

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Balance Type:	credit
Period Type:	instant

- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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Balance Type:	na
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- Definition

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

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(2))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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Balance Type:	na
Period Type:	duration

- Definition

Percentage price of original principal amount of debt at which debt can be redeemed by the issuer.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 50
-Paragraph 3
-Subparagraph e
-URI http://asc.fasb.org/extlink&oid=6479336&loc=d3e64711-112823

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Balance Type:	na
Period Type:	duration

- Definition

Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

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

- Definition

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

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28555-108399

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-Name Accounting Standards Codification
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-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.17)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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

- Definition

The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=66011266&loc=d3e33918-111571

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Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

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

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(16))
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-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
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-Publisher FASB
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-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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

- References

No definition available.

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

- 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

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

- Definition

The cash outflow during the period from the repayment of aggregate short-term and long-term debt. Excludes payment of capital lease obligations.

+ References

No definition available.

+ Details

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

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Debt (Details) - USD ($) $ / shares in Units, $ in Thousands, shares in Millions			3 Months Ended
	Mar. 18, 2016	May 31, 2011	Mar. 31, 2017	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2016	Aug. 15, 2016	Nov. 30, 2015	May 04, 2015
Long-term debt [Abstract]
Carrying value			$ 223,970		$ 294,103	$ 233,955
Prepayment of debt			10,000		0
Maximum amount of debt and equity to be issued under shelf registration									$ 500,000
Amount available for debt and equity issuance under shelf registration			500,000
Level 2 [Member]
Long-term debt [Abstract]
Fair value			227,124		293,085	237,013
4.5% Convertible Notes [Member]
Long-term debt [Abstract]
Carrying value			$ 109,844		$ 0	$ 109,835
Debt instrument, interest rate			4.50%		4.50%	4.50%	4.50%
Debt instrument, term			5 years
Face value of debt							$ 110,000
Debt instrument, maturity date			Aug. 15, 2021
Debt issuance costs			$ 156		$ 0	$ 165	$ 174
4.5% Convertible Notes [Member] \| Common Class A [Member]
Long-term debt [Abstract]
Debt instrument, conversion price (in dollars per share)							$ 55.00
Debt instrument, shares issuable in conversion (in shares)							2
4.5% Convertible Notes [Member] \| Level 2 [Member]
Long-term debt [Abstract]
Fair value			$ 111,634		0	111,525
4.5% Convertible Notes [Member] \| GGCP Holdings LLC [Member]
Long-term debt [Abstract]
Equity method investment, ownership percentage							63.00%
Period of interest included in initial deposit			6 months
AC 4% PIK Note [Member]
Long-term debt [Abstract]
Carrying value			$ 90,000		250,000	100,000
Debt instrument, interest rate			4.00%					4.00%
Face value of debt			$ 90,000					$ 250,000
Debt instrument, maturity date			Nov. 30, 2020
AC 4% PIK Note [Member] \| Principal Amount Due on November 30, 2017 [Member]
Long-term debt [Abstract]
Prepayment of debt			$ 10,000
AC 4% PIK Note [Member] \| Principal Amount Due on November 30, 2018 [Member]
Long-term debt [Abstract]
Face value of debt			20,000
AC 4% PIK Note [Member] \| Principal Amount Due on November 30, 2019 [Member]
Long-term debt [Abstract]
Face value of debt			20,000
AC 4% PIK Note [Member] \| Principal Amount Due on November 30, 2020 [Member]
Long-term debt [Abstract]
Face value of debt			50,000
AC 4% PIK Note [Member] \| Level 2 [Member]
Long-term debt [Abstract]
Fair value			90,932		249,183	100,930
Loan from GGCP [Member]
Long-term debt [Abstract]
Carrying value			$ 0		20,000	0
Debt instrument, term			1 year
Face value of debt			$ 35,000
Debt instrument, maturity date			Dec. 28, 2016
Repayment of debt	$ 15,000			$ 20,000
Loan from GGCP [Member] \| 90-day LIBOR [Member]
Long-term debt [Abstract]
Debt instrument, basis spread on variable rate			3.25%
Debt instrument term of variable rate			90 days
Loan from GGCP [Member] \| Level 2 [Member]
Long-term debt [Abstract]
Fair value			$ 0		20,161	0
5.875% Senior Notes [Member]
Long-term debt [Abstract]
Carrying value			$ 24,126		$ 24,103	$ 24,120
Debt instrument, interest rate		5.875%	5.875%		5.875%	5.875%
Debt instrument, term			10 years
Face value of debt		$ 100,000
Debt instrument, maturity date			Jun. 01, 2021
Debt issuance costs			$ 99		$ 122	$ 105
Debt redemption price		101.00%
5.875% Senior Notes [Member] \| Level 2 [Member]
Long-term debt [Abstract]
Fair value			$ 24,558		$ 23,741	$ 24,558