Related Party Transactions - Schedule of related party transactions activity (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2015 USD ($) management_company		Dec. 31, 2014 USD ($) management_company	Dec. 31, 2013 USD ($)
Related Party Transaction [Line Items]
Reported net premiums written	$ 7,951,063		$ 5,944,841	$ 6,199,404
Net losses and loss expenses incurred	4,766,200		3,258,393	3,731,464
Reported acquisition costs	$ 1,317,448	[1]	$ 738,118	909,323
Number of investment management companies | management_company	6		6
Other strategic affiliates or subsidiaries
Related Party Transaction [Line Items]
Reported net premiums written	$ 42,042		$ 91,261	73,085
Net losses and loss expenses incurred	13,246		38,927	29,042
Reported acquisition costs	$ 14,682		$ 35,711	$ 25,275

[1] The Company has reflected the amortization of certain fair value adjustments recorded in conjunction with the Catlin Acquisition within the respective segments.