Derivative Instruments (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Derivative [Line Items]
Cash collateral payable to trade counterparties	$ 8,500		$ 300
Cash collateral received	9,600		4,300
Gain (loss) on equity options activity	18,400	$ (7,600)
Exchange-traded options \| Long
Derivative [Line Items]
Cash collateral payable to trade counterparties	0		0
Long exchange-traded equity options	36,800		6,900
Exchange-traded options \| Short
Derivative [Line Items]
Cash collateral received	0		0
Short exchange-traded equity options, included in securities sold not yet purchased	$ 15,900		$ 12,300

Amount of obligation to return cash collateral under master netting arrangements that have not been offset against derivative assets.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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Amount of right to receive cash collateral under master netting arrangements that have not been offset against derivative liabilities.

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Fair value as of the balance sheet date of derivative instrument not designated as hedging instrument and classified as an asset.

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Fair value as of the balance sheet date of derivative instrument not designated as hedging instrument and classified as a liability.

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Aggregate net gain and losses (whether realized or unrealized) on all derivative instruments held for trading purposes whether or not settled physically.

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