Collateralized Reinsurance And Trust Agreements (Narrative) (Details) $ in Thousands							12 Months Ended
	Dec. 12, 2019 USD ($) Item	Apr. 30, 2018 USD ($) Item	Apr. 13, 2017 USD ($) Item	Dec. 01, 2015 USD ($) Item	Nov. 18, 2014 USD ($)	Apr. 24, 2014 USD ($) Item	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Effects of Reinsurance [Line Items]
Amount on deposit in trust accounts							$ 718,548
Reinsurance coverage amount							$ 1,278,115	$ 1,541,814	$ 3,064,645
Kilimanjaro Re Limited [Member]
Effects of Reinsurance [Line Items]
Number of collateralized reinsurance agreements | Item		4	6	2		2
Reinsurance contract expiration						Apr. 01, 2018
Kilimanjaro Re Limited [Member] | Catastrophe Reinsurance [Member]
Effects of Reinsurance [Line Items]
Number of collateralized reinsurance agreements | Item	4
Reinsurance coverage amount					$ 500,000
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 1-2 [Member]
Effects of Reinsurance [Line Items]
Number of collateralized reinsurance agreements | Item	2	2
Reinsurance Contracts	4 years	4 years
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 1 [Member]
Effects of Reinsurance [Line Items]
Reinsurance coverage amount	$ 150,000	$ 62,500	$ 225,000	$ 300,000
Kilimanjaro Re Limited [Member] | Catastrophe Reinsurance Agreement 2 [Member]
Effects of Reinsurance [Line Items]
Reinsurance coverage amount	$ 275,000	$ 200,000	400,000	325,000
Kilimanjaro Re Limited [Member] | Catastrophe Reinsurance Agreement 3-4 [Member]
Effects of Reinsurance [Line Items]
Number of collateralized reinsurance agreements | Item	2	2
Reinsurance Contracts	5 years	5 years
Kilimanjaro Re Limited [Member] | Catastrophe Reinsurance Agreement 3 [Member]
Effects of Reinsurance [Line Items]
Reinsurance coverage amount	$ 150,000	$ 62,500	$ 325,000
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
Kilimanjaro Re Limited [Member] | Catastrophe Reinsurance Agreement 4 [Member]
Effects of Reinsurance [Line Items]
Reinsurance coverage amount	275,000	200,000	$ 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
Series 2014-1 Notes [Member] | Kilimanjaro Re Limited [Member] | Catastrophe Reinsurance [Member]
Effects of Reinsurance [Line Items]
Catastrophe reinsurance bonds, funded amount						$ 450,000
Catastrophe Reinsurance Bonds Redeemed Amount		450,000
Series 2014-2 Notes [Member] | Kilimanjaro Re Limited [Member] | Catastrophe Reinsurance [Member]
Effects of Reinsurance [Line Items]
Catastrophe reinsurance bonds, funded amount					$ 500,000
Series 2015-1 Notes [Member] | Kilimanjaro Re Limited [Member] | Catastrophe Reinsurance [Member]
Effects of Reinsurance [Line Items]
Catastrophe reinsurance bonds, funded amount				$ 625,000
Series 2017-1 Notes [Member] | Kilimanjaro Re Limited [Member] | Catastrophe Reinsurance [Member]
Effects of Reinsurance [Line Items]
Catastrophe reinsurance bonds, funded amount			950,000
Series 2017-2 Notes [Member] | Kilimanjaro Re Limited [Member] | Catastrophe Reinsurance [Member]
Effects of Reinsurance [Line Items]
Catastrophe reinsurance bonds, funded amount			$ 300,000
Series 2018-1 Notes [Member] | Kilimanjaro Re Limited [Member] | Catastrophe Reinsurance [Member]
Effects of Reinsurance [Line Items]
Catastrophe reinsurance bonds, funded amount		262,500
Series 2018-2 Notes [Member] | Kilimanjaro Re Limited [Member] | Catastrophe Reinsurance [Member]
Effects of Reinsurance [Line Items]
Catastrophe reinsurance bonds, funded amount		$ 262,500
Series 2019-1 Notes [Member] | Kilimanjaro Re Limited [Member]
Effects of Reinsurance [Line Items]
Catastrophe reinsurance bonds, funded amount	425,000
Series 2019-2 Notes [Member] | Kilimanjaro Re Limited [Member]
Effects of Reinsurance [Line Items]
Catastrophe reinsurance bonds, funded amount	$ 425,000