Goodwill and Other Intangible Assets (Narrative) (Details) - USD ($) $ in Thousands |
12 Months Ended | |||
---|---|---|---|---|
Dec. 31, 2017 |
Dec. 31, 2016 |
Dec. 31, 2015 |
Mar. 02, 2015 |
|
Minimum | ||||
Goodwill and Intangible Assets [Line Items] | ||||
Finite-lived intangible assets, useful life | 1 year | |||
Maximum | ||||
Goodwill and Intangible Assets [Line Items] | ||||
Finite-lived intangible assets, useful life | 16 years | |||
Weighted Average | ||||
Goodwill and Intangible Assets [Line Items] | ||||
Finite-lived intangible assets, useful life | 7 years 10 months 24 days | |||
Investments in other ventures, under equity method | ||||
Goodwill and Intangible Assets [Line Items] | ||||
Goodwill | $ 7,818 | $ 7,818 | $ 7,818 | |
Platinum Underwriters Holdings, Ltd. | ||||
Goodwill and Intangible Assets [Line Items] | ||||
Goodwill | $ 191,729 | |||
Finite lived intangible assets acquired | 75,200 | |||
Indefinite lived intangible assets acquired | $ 8,400 |