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Fair Value Measurements - Investments in Company-Sponsored Funds (Details) $ in Thousands | 12 Months Ended
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Dec. 31, 2017 USD ($)
Investment Holdings [Line Items] |  |
Fair Value | $ 7,617 |
Unfunded Commitments | 1,400 |
Hedge Funds [Member] |  |
Investment Holdings [Line Items] |  |
Fair Value | 2,618 | [1]
Unfunded Commitments | $ 0 | [1]
Redemption Frequency | Quarterly - Annually | [1]
Private Equity Funds |  |
Investment Holdings [Line Items] |  |
Investments Lock In Period | 10 years |
Fair Value | $ 4,999 | [2]
Unfunded Commitments | $ 1,400 | [2]
[1] | Includes investments in hedge funds and hedge fund of funds that pursue long/short, event-driven, and activist strategies. Each hedge fund has various restrictions regarding redemption; no investment is locked-up for a period greater than one year.
[2] | Includes private equity funds and private equity fund of funds with a focus on diversified portfolios, real estate and global natural resources. Due to the illiquid nature of these funds, investors are not permitted to make withdrawals without the consent of the general partner. The lock-up period of the private equity funds can extend to 10 years.

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