Fair Value of Financial Instruments - Summary of Estimated Fair Values of Investments and Remaining Unfunded Commitments for Each Major Category of Investments (Details) $ in Thousands	Dec. 31, 2018 USD ($)
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Carrying Amount	$ 469,599
Fair Value	469,599
Unfunded Commitments	18,802
Non-marketable securities \| Consolidated venture capital and private equity fund investments \| Fair value accounting
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Carrying Amount	318,352
Fair Value	318,352
Unfunded Commitments	12,973
Non-marketable securities \| Consolidated venture capital and private equity fund investments \| Equity method accounting
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Carrying Amount	129,485
Fair Value	129,485
Unfunded Commitments	4,943
Non-marketable securities \| Debt funds \| Equity method accounting
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Carrying Amount	5,826
Fair Value	5,826
Unfunded Commitments	0
Non-marketable securities \| Other investments \| Equity method accounting
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Carrying Amount	15,936
Fair Value	15,936
Unfunded Commitments	$ 886

Carrying Amount, Investments, Entities that Calculate Net Asset Value Per Share, Planned Sale, Investments Not Identified, Value

No definition available.

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- 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.

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- Definition

The total fair value for all investments, comprising or included in the major category, of those certain investments for which net asset value per share is calculated (including by unit, membership interest, or other equity (ownership interest) unit measure) (alternative investments) for which the entity has intentions to sell or liquidate, but the specific assets for sale or liquidation have not been identified (for example, the entity intends to sell $10,000,000 of its investments in private equity funds, but the individual investments to be sold have not been identified).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 6A
-Subparagraph (h)
-URI http://asc.fasb.org/extlink&oid=99377789&loc=SL6742756-110258

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- Definition

The amount of unfunded commitments for which the entity is obligated, to those certain investments for which net asset value per share is calculated (including by unit, membership interest, or other equity (ownership interest) unit measure) (alternative investments).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 6A
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=99377789&loc=SL6742756-110258

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