Acquisition of Tokio Millennium Re (Schedule of Supplemental Pro Forma Information) (Details) - TMR - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Business Acquisition [Line Items]
Total revenues	$ 4,542,979	$ 3,338,903
Net income available to RenaissanceRe common shareholders	$ 768,719	$ 281,974