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v3.10.0.1

Fair Value Measurement (Narrative) (Details) | 3 Months Ended | 6 Months Ended | 12 Months Ended
--- | --- | --- | ---
Jun. 30, 2018 USD ($) Agreement | Jun. 30, 2017 USD ($) | Jun. 30, 2018 USD ($) Agreement | Jun. 30, 2017 USD ($) | Dec. 31, 2017 USD ($)
Credit Derivatives [Line Items] |  |  |  |  |
Transfer of equity securities from Level 2 to Level 1 | $ 0 | $ 35,400,000 | $ 0 | $ 35,400,000 |
Net impairment losses recognized in earnings | 404,000 | $ 0 | 404,000 | $ 171,000 |
Fair value of funded deferred compensation assets | $ 22,300,000 |  | $ 22,300,000 |  | $ 20,200,000
Number of line of credit agreement | Agreement | 2 |  | 2 |  |
Corporate debt, limited observable inputs | NRSRO | NRSRO, Rating BBB |  |  |  |  |
Credit Derivatives [Line Items] |  |  |  |  |
Credit rating |  |  | 76.00% |  |
Corporate debt, limited observable inputs | NRSRO | NRSRO, Rating BBBplus |  |  |  |  |
Credit Derivatives [Line Items] |  |  |  |  |
Credit rating |  |  |  |  | 84.00%
Residential mortgage-backed and other asset-backed securities | NRSRO | NRSRO, Rating AAA |  |  |  |  |
Credit Derivatives [Line Items] |  |  |  |  |
Credit rating |  |  | 70.00% |  | 21.00%
Early Stage Business Development | Investment in unconsolidated subsidiaries |  |  |  |  |
Credit Derivatives [Line Items] |  |  |  |  |
Net impairment losses recognized in earnings |  |  |  |  | $ 8,500,000
Fair Value, Measurements, Nonrecurring |  |  |  |  |
Credit Derivatives [Line Items] |  |  |  |  |
Fair value, net asset (liability) | $ 0 |  | $ 0 |  | $ 1,200,000

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