The conversion price as a percent of the volume-weighted average conversion price.

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The maximum amount of dividends that the entity may declare after the second anniversary under debt covenants.

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Threshold period of specified consecutive trading days within which common stock price to conversion price of convertible debt instrument must exceed threshold percentage for specified number of trading days to trigger reset conversion price.

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Internal rate of return realized from date of issuance.

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The maximum amount of dividends that the entity may declare through the second anniversary until debt covenants.

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The percentage of shares issuable upon a conversion to the outstanding fully-diluted share capital.

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Carrying amount of long-term convertible debt as of the balance sheet date, net of the amount due in the next twelve months or greater than the normal operating cycle, if longer. The debt is convertible into another form of financial instrument, typically the entity's common stock.

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

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

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The amount by which the convertible debt's if-converted value exceeds its principle amount at the balance sheet date, regardless of whether the instrument is currently convertible. This element applies to public companies only.

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The number of equity instruments that the holder of the debt instrument would receive if the debt was converted to equity.

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Minimum percentage of common stock price to conversion price of convertible debt instruments to determine eligibility of conversion.

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Threshold number of specified trading days that common stock price to conversion price of convertible debt instruments must exceed threshold percentage within a specified consecutive trading period to trigger conversion feature.

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Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

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

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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.

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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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Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

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Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

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Amount of increase (decrease) of financial instrument classified as a derivative asset (liability) after deduction of derivative liability (asset), measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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

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Amount of income (expense) related to nonoperating activities, classified as other.

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Price of a single share of a number of saleable stocks of a company.

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CORPORATE BORROWINGS - Senior Unsecured Convertible Notes narrative (Details)			3 Months Ended
	Sep. 30, 2018 item	Sep. 14, 2018 USD ($) item $ / shares	Mar. 31, 2020 USD ($) $ / shares	Mar. 31, 2019 USD ($)	Dec. 31, 2019 USD ($)	Sep. 04, 2018 USD ($)
CORPORATE BORROWINGS
Derivative liability					$ 500,000
Debt issuance costs			$ 84,500,000		88,800,000
Interest expense			71,300,000	$ 71,300,000
Other expense			(26,900,000)	(29,800,000)
Class B common stock
CORPORATE BORROWINGS
Price per share (in dollars per share) \| $ / shares		$ 17.50
2.95% Senior Unsecured Convertible Notes due 2024
CORPORATE BORROWINGS
Principal balance		$ 600,000,000.0	$ 600,000,000.0		$ 600,000,000.0
Stated interest rate (as a percent)		2.95%	2.95%		2.95%
Change fair value of derivative			$ 500,000	13,300,000
If-converted value in excess of principal			$ 499,900,000
Price per share (in dollars per share) \| $ / shares			$ 3.16
Derivative liability		$ 90,400,000			$ 500,000
Effective interest rate		5.98%
Debt issuance costs		$ 13,600,000	$ 10,800,000		$ 11,200,000
Interest expense			8,300,000	8,000,000.0
Other expense			$ 20,100,000	$ 15,100,000
Maximum dividends allowed through the second anniversary of issuance \| $ / shares		$ 0.20
Maximum dividends allowed after the second anniversary of issuance \| $ / shares		$ 0.10
Threshold percentage of stock price trigger		150.00%
Debt Instrument, Convertible, Threshold Trading Days \| item		20
Debt Instrument, Convertible, Threshold Consecutive Trading Days \| item		30
Internal rate of return		15.00%
2.95% Senior Unsecured Convertible Notes due 2024 \| Class A common stock
CORPORATE BORROWINGS
Conversion rate		52.7704
Conversion rate (in dollars per share) \| $ / shares		$ 18.95	$ 18.95
Number of shares upon conversion	31,662,269		31,662,269
Minimum conversion price percentage causing a reset conversion price		120.00%
Number of days needed to cause a reset conversion price			10 days
Maximum allowed percentage of outstanding fully-diluted share capital resulting a conversion price floor		30.00%
2.95% Senior Unsecured Convertible Notes due 2024 \| Class B common stock
CORPORATE BORROWINGS
Number of shares upon conversion \| item		5,666,000
Derivative Asset						$ 10,700,000