Fair Value Measurements (Quantitative Information Used As Level 3 Inputs) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Total other assets and (liabilities)	$ 2,533	$ 2,542
Internal valuation model | Fair Value (Level 3)
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Total other assets and (liabilities)	2,780
Assumed and ceded (re)insurance contracts, group one | Internal valuation model | Fair Value (Level 3)
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Other assets	$ 893
Assumed and ceded (re)insurance contracts, group one | Internal valuation model | Fair Value (Level 3) | Low
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Bond price (in dollars per share)	$ 101.46
Assumed and ceded (re)insurance contracts, group one | Internal valuation model | Fair Value (Level 3) | High
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Bond price (in dollars per share)	112.05
Assumed and ceded (re)insurance contracts, group one | Internal valuation model | Fair Value (Level 3) | Weighted Average or Actual
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Bond price (in dollars per share)	$ 107.31
Liquidity discount	1.30%
Assumed and ceded (re)insurance contracts, group two | Internal valuation model | Fair Value (Level 3)
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Other (liabilities)	$ (3,673)
Assumed and ceded (re)insurance contracts, group two | Internal valuation model | Fair Value (Level 3) | Low
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Contract period	2 years
Assumed and ceded (re)insurance contracts, group two | Internal valuation model | Fair Value (Level 3) | High
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Contract period	4 years 8 months 12 days
Assumed and ceded (re)insurance contracts, group two | Internal valuation model | Fair Value (Level 3) | Weighted Average or Actual
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Net undiscounted cash flows	$ (4,706)
Expected loss ratio	20.40%
Net acquisition expense ratio	13.70%
Contract period	4 years 1 month 6 days
Discount rate	2.40%