Notes Payable and Debt and Financing Arrangements - Letter of credit facilities and other sources of collateral (Details) $ in Thousands, AUD in Millions		Jun. 30, 2015 USD ($) Credit_Facilities		Jun. 30, 2015 AUD Credit_Facilities	Dec. 31, 2014 USD ($) Credit_Facilities
Line of Credit Facility [Line Items]
Number of letter of credit facilities available | Credit_Facilities		18		18	8
Revolving credit facility
Line of Credit Facility [Line Items]
Available credit facilities - remaining borrowing capacity	[1],[2],[3]	$ 1,032,100			$ 968,900
Available letter of credit facilities - commitments		1,700,000			1,600,000
Available letter of credit facilities - in use		667,900			606,100
November 2013 credit agreement
Line of Credit Facility [Line Items]
Available credit facilities - remaining borrowing capacity		976,100			968,900
Available letter of credit facilities - commitments		1,000,000
Letter of credit facilities
Line of Credit Facility [Line Items]
Available letter of credit facilities - commitments	[2],[4]	4,855,000			3,575,000
Available letter of credit facilities - in use		$ 2,585,348	[2]		$ 1,790,561	[5]
Collateralized by certain assets of the Company’s investment portfolio	[2]	50.20%		50.20%	66.20%
2013 Citi agreements | Revolving credit facility
Line of Credit Facility [Line Items]
Available letter of credit facilities - commitments		$ 550,000			$ 575,000
2013 Citi agreements | Letter of credit facilities
Line of Credit Facility [Line Items]
Available letter of credit facilities - in use		550,000
Syndicated credit agreements
Line of Credit Facility [Line Items]
Optional increased capacity		500,000
Catlin Group Limited
Line of Credit Facility [Line Items]
Available letter of credit facilities - in use		1,000
Catlin Group Limited | Unsecured multi-bank facility
Line of Credit Facility [Line Items]
Available letter of credit facilities - commitments		450,000
Catlin Group Limited | Letter of credit facilities
Line of Credit Facility [Line Items]
Available letter of credit facilities - in use		8,000
Catlin Group Limited | Bilateral facility
Line of Credit Facility [Line Items]
Available credit facilities - remaining borrowing capacity		56,000
Available letter of credit facilities - commitments		$ 150,000		AUD 50
Number of letter of credit facilities available | Credit_Facilities		2		2
Catlin Bermuda | Bilateral facility
Line of Credit Facility [Line Items]
Available letter of credit facilities - in use		$ 147,000
Catlin Bermuda | LLoyd's syndicate | Bilateral facility
Line of Credit Facility [Line Items]
Available letter of credit facilities - commitments		$ 375,000
Number of letter of credit facilities available | Credit_Facilities		4		4
Catlin Re Switzerland | Bilateral facility
Line of Credit Facility [Line Items]
Available letter of credit facilities - in use		$ 49,000

[1] As of June 30, 2015 and December 31, 2014, $976.1 million and $968.9 million, respectively, of revolving credit was available under the Company's syndicated unsecured credit agreement, which currently provides for up to $1 billion of revolving credit loans. The Company has the option to increase the size of the facilities under the syndicated secured and unsecured credit agreements by an additional $500 million across both facilities. Two bilateral facilities assumed as a result of the Catlin Acquisition with commitments totaling $150.0 million also provide for revolving credit loans. As of June 30, 2015, $56.0 million of revolving credit was available to draw under these facilities.

[2] As of June 30, 2015 and December 31, 2014, there were eighteen and eight available letter of credit facilities, respectively.

[3] The credit agreements initially entered into with Citicorp USA, Inc. in May through November 2013 (the "Citi Agreements") provide for issuance of letters of credit and revolving credit loans up to an aggregate amount of $550.0 million, compared to $575.0 million as of December 31, 2014. As of June 30, 2015, $550.0 million of letters of credit were issued under these agreements, and therefore no amounts are included in this line as available to draw under this facility. The Company also has the option to increase the maximum amount of the letters of credit and revolving credit loans available under the Citi Agreements with the lender's and issuing lender's consent.

[4] The available letter of credit facilities include approximately $1 billion that is also included in the "revolving credit facilities" line in this table.

[5] "In Use" and "Outstanding" data represent June 30, 2015 and December 31, 2014 accreted values.