Notes Payable and Debt and Financing Arrangements - Narrative relating to credit facilities (Details) $ in Thousands		1 Months Ended
		Nov. 30, 2013 USD ($) Credit_Facilities	Dec. 31, 2015 USD ($) Credit_Facilities	Dec. 31, 2014 USD ($) Credit_Facilities	Dec. 30, 2014 USD ($)
Line of Credit Facility [Line Items]
Number of letter of credit facilities available | Credit_Facilities			15	8
Funds at Lloyds Bilateral Facility [Member]
Line of Credit Facility [Line Items]
Number of letter of credit facilities available | Credit_Facilities			4
Available letter of credit facilities - commitments			$ 500,000
Funds at Lloyds Bilateral Facility I [Member]
Line of Credit Facility [Line Items]
Available letter of credit facilities - commitments			125,000
Funds at Lloyds Bilateral Facility II [Member]
Line of Credit Facility [Line Items]
Available letter of credit facilities - commitments			125,000
Funds at Lloyds Bilateral Facility III [Member]
Line of Credit Facility [Line Items]
Available letter of credit facilities - commitments			125,000
Funds at Lloyds Bilateral Facility IV [Member]
Line of Credit Facility [Line Items]
Available letter of credit facilities - commitments			125,000
Two Thousand Thirteen Citi Agreements [Member]
Line of Credit Facility [Line Items]
Available letter of credit facilities - commitments			350,000
Revolving credit facility
Line of Credit Facility [Line Items]
Available letter of credit facilities - in use			527,100	$ 606,100
Available letter of credit facilities - commitments			1,400,000	1,600,000
Line of credit facility, remaining borrowing capacity			822,900	968,900
Syndicated Credit Agreements [Member]
Line of Credit Facility [Line Items]
Available letter of credit facilities - commitments		$ 2,000,000
Optional increase capacity			500,000
Number of credit facilities entered into | Credit_Facilities		2
Two Thousand Thirteen Secured Credit Agreement [Member]
Line of Credit Facility [Line Items]
Available letter of credit facilities - commitments			1,000,000
Letter of credit facility
Line of Credit Facility [Line Items]
Available letter of credit facilities - in use	[1]		2,515,653	1,790,561
Available letter of credit facilities - commitments	[1],[2]		4,463,041	$ 3,575,000
Two Thousand Thirteen Unsecured Credit Agreement [Member]
Line of Credit Facility [Line Items]
Available letter of credit facilities - commitments			1,000,000
Twenty Fifteen Goldman Sachs Facility [Member]
Line of Credit Facility [Line Items]
Available letter of credit facilities - commitments			200,000
Catlin Bermuda [Member] | Bilateral Facility [Member]
Line of Credit Facility [Line Items]
Available letter of credit facilities - in use			230,000
Catlin Re Switzerland [Member] | Bilateral Facility [Member]
Line of Credit Facility [Line Items]
Available letter of credit facilities - in use			175,000
Catlin Group Limited [Member] | Letter of credit facility
Line of Credit Facility [Line Items]
Available letter of credit facilities - in use			8,000
Citibank Europe plc [Member] | Letter of credit facility
Line of Credit Facility [Line Items]
Available letter of credit facilities - in use			600,000		$ 750,000
ING Bank N.V., London Branch [Member] | Letter of credit facility
Line of Credit Facility [Line Items]
Available letter of credit facilities - in use			$ 150,000
Lloyds Syndicate | Catlin Bermuda [Member] | Bilateral Facility [Member]
Line of Credit Facility [Line Items]
Number of letter of credit facilities available | Credit_Facilities			4
Citibank N.A. [Member] | Letter of credit facility
Line of Credit Facility [Line Items]
Available letter of credit facilities - in use			$ 250,000

[1] As of December 31, 2015 and December 31, 2014, there were fifteen and eight available credit facilities, respectively.

[2] As of December 31, 2015 and December 31, 2014 the stated portion of allowable credit facilities permitted to be utilized for revolving loans was $1.4 billion and $1.6 billion, respectively. However, as of December 31, 2015 and December 31, 2014, $527.1 million and $606.1 million, respectively, of such facilities' limits were utilized to issue letters of credit, leaving $822.9 million and $968.9 million, respectively, available either to issue additional letters of credit or to support other operating or financing needs under these particular facilities.