Noncontrolling Interests (Summary of Redeemable Noncontrolling Interest) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Redeemable Noncontrolling Interest [Line Items]
Redeemable noncontrolling interests	$ 2,051,700	$ 1,296,506
Net income (loss) attributable to redeemable noncontrolling interest	41,553	(132,282)	$ 127,086
DaVinciRe Holdings Ltd.
Redeemable Noncontrolling Interest [Line Items]
Redeemable noncontrolling interests	1,034,946	1,011,659	994,458
Net income (loss) attributable to redeemable noncontrolling interest	27,638	(134,860)	118,748
RenaissanceRe Medici Fund Ltd.
Redeemable Noncontrolling Interest [Line Items]
Redeemable noncontrolling interests	416,765	284,847	181,136
Net income (loss) attributable to redeemable noncontrolling interest	13,926	2,578	8,338
Vermeer Reinsurance Ltd.
Redeemable Noncontrolling Interest [Line Items]
Redeemable noncontrolling interests	599,989	0	0
Net income (loss) attributable to redeemable noncontrolling interest	$ (11)	$ 0	$ 0