Variable Interest Entities and Noncontrolling Interests - Non-redeemable noncontrolling interests (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Noncontrolling Interest [Line Items]
Non-redeemable noncontrolling interests, beginning of period			$ 851,854
Amounts attributable to noncontrolling interests	$ 9,346	$ 33,716	25,670	$ 49,958
Non-redeemable noncontrolling interests, end of period	877,456	788,589	877,456	788,589
Watford Re
Noncontrolling Interest [Line Items]
Non-redeemable noncontrolling interests, beginning of period	868,186	754,915	851,854	738,831
Amounts attributable to noncontrolling interests	9,346	33,716	25,670	49,958
Foreign currency translation adjustments attributable to noncontrolling interests	(76)	(42)	(68)	(200)
Non-redeemable noncontrolling interests, end of period	$ 877,456	$ 788,589	$ 877,456	$ 788,589
Common shares | Watford Re
Noncontrolling Interest [Line Items]
Noncontrolling interest, ownership percentage by noncontrolling owners	89.00%		89.00%