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Fair Value (Fair Value Measurements Using Significant Unobservable Inputs For Equity Index Put Option Contracts) (Details) - USD ($)
$ in Thousands
3 Months Ended
Mar. 31, 2019
Mar. 31, 2018
Fair Value [Abstract]    
Balance, beginning of period $ 11,958 $ 12,477
Total (gains) or losses (realized/unrealized) Included in earnings (3,231) (273)
Balance, end of period $ 8,727 $ 12,205