Subsequent Events (Narrative) (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended
	Oct. 25, 2017	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Subsequent Event [Line Items]
Estimated net incurred losses		$ 1,075,432	$ 579,405	$ 2,210,129	$ 1,564,925
California Wildfires [Member] | Minimum [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Estimated net incurred losses	$ 40,000
California Wildfires [Member] | Maximum [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Estimated net incurred losses	$ 80,000