Fair Value Measurements (Quantitative Information Used As Level 3 Inputs) (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Total other assets and (liabilities)	$ 2,542	$ 4,379
Significant Unobservable Inputs (Level 3)
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Total other assets and (liabilities)	(2,952)
Significant Unobservable Inputs (Level 3) | Assumed reinsurance contract | Internal Valuation Model Valuation Technique
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Other assets and (liabilities)	$ 850
Significant Unobservable Inputs (Level 3) | Assumed reinsurance contract | Internal Valuation Model Valuation Technique | Low
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Assumed and ceded (re)insurance contracts, Bond price, Unobservable and Observable Inputs (in usd per share)	$ 101.53
Significant Unobservable Inputs (Level 3) | Assumed reinsurance contract | Internal Valuation Model Valuation Technique | Maximum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Assumed and ceded (re)insurance contracts, Bond price, Unobservable and Observable Inputs (in usd per share)	111.56
Significant Unobservable Inputs (Level 3) | Assumed reinsurance contract | Internal Valuation Model Valuation Technique | Weighted average or actual
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Assumed and ceded (re)insurance contracts, Bond price, Unobservable and Observable Inputs (in usd per share)	$ 107.15
Liquidity discount	1.30%
Significant Unobservable Inputs (Level 3) | Assumed and ceded (re)insurance contracts | Internal Valuation Model Valuation Technique
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Assumed and ceded (re)insurance contracts	$ 3,802
Significant Unobservable Inputs (Level 3) | Assumed and ceded (re)insurance contracts | Internal Valuation Model Valuation Technique | Low
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Contract period	2 years
Significant Unobservable Inputs (Level 3) | Assumed and ceded (re)insurance contracts | Internal Valuation Model Valuation Technique | Maximum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Contract period	4 years 8 months 12 days
Significant Unobservable Inputs (Level 3) | Assumed and ceded (re)insurance contracts | Internal Valuation Model Valuation Technique | Weighted average or actual
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Net undiscounted cash flows	$ (4,626)
Expected loss ratio	22.10%
Net acquisition expense ratio	13.50%
Contract period	4 years 1 month 6 days
Discount rate	2.20%