Collateralized Reinsurance And Trust Agreements (Narrative) (Details) $ in Thousands					6 Months Ended
	Apr. 13, 2017 USD ($) item	Dec. 01, 2015 USD ($) item	Nov. 18, 2014 USD ($)	Apr. 24, 2014 USD ($) item	Jun. 30, 2017 USD ($)
Effects of Reinsurance [Line Items]
Amount on deposit in trust accounts					$ 649,841
Kilimanjaro Re Limited [Member]
Effects of Reinsurance [Line Items]
Number of collateralized reinsurance agreements | item	6	2		2
Kilimanjaro Re Limited [Member] | Catastrophe Reinsurance [Member]
Effects of Reinsurance [Line Items]
Reinsurance coverage amount			$ 500,000
Catastrophe reinsurance bonds, funded amount		$ 625,000	$ 500,000	$ 450,000
Kilimanjaro Re Limited [Member] | Catastrophe Reinsurance [Member] | Southeastern United States [Member]
Effects of Reinsurance [Line Items]
Reinsurance coverage amount				250,000
Kilimanjaro Re Limited [Member] | Catastrophe Reinsurance [Member] | Southeast, Mid-Atlantic And Northeast United States And Puerto Rico [Member]
Effects of Reinsurance [Line Items]
Reinsurance coverage amount				$ 200,000
Kilimanjaro Re Limited [Member] | Catastrophe Reinsurance Agreement 1 [Member]
Effects of Reinsurance [Line Items]
Reinsurance coverage amount	$ 225,000	300,000
Catastrophe reinsurance bonds, funded amount	950,000
Kilimanjaro Re Limited [Member] | Catastrophe Reinsurance Agreement 2 [Member]
Effects of Reinsurance [Line Items]
Reinsurance coverage amount	400,000	$ 325,000
Catastrophe reinsurance bonds, funded amount	300,000
Kilimanjaro Re Limited [Member] | Catastrophe Reinsurance Agreement 3 [Member]
Effects of Reinsurance [Line Items]
Reinsurance coverage amount	$ 325,000
Kilimanjaro Re Limited [Member] | Catastrophe Reinsurance Agreements 1- 3 [Member]
Effects of Reinsurance [Line Items]
Number of collateralized reinsurance agreements | item	3
Reinsurance Contracts					4 years
Kilimanjaro Re Limited [Member] | Catastrophe Reinsurance Agreement 4 [Member]
Effects of Reinsurance [Line Items]
Reinsurance coverage amount	$ 50,000
Kilimanjaro Re Limited [Member] | Catastrophe Reinsurance Agreement 5 [Member]
Effects of Reinsurance [Line Items]
Reinsurance coverage amount	75,000
Kilimanjaro Re Limited [Member] | Catastrophe Reinsurance Agreement 6 [Member]
Effects of Reinsurance [Line Items]
Reinsurance coverage amount	$ 175,000
Kilimanjaro Re Limited [Member] | Catastrophe Reinsurance Agreements 4 - 6 [Member]
Effects of Reinsurance [Line Items]
Number of collateralized reinsurance agreements | item	3
Reinsurance Contracts					5 years