Acquisition and Disposals - Fair value of assets and liabilities acquired (Details) - USD ($) $ in Thousands			6 Months Ended
		May. 01, 2015	Jun. 30, 2015
LIABILITIES
Goodwill			$ 778,043
Catlin Group Limited
ASSETS
Fixed maturities, at fair value		$ 6,266,489
Short-term investments, at fair value		634,599
Equity investments, at fair value		236,230
Investment in affiliates		216,843
Other investments		386,828
Total investments		7,740,989
Cash and cash equivalents (1)	[1]	1,267,565
Unpaid losses and loss expenses recoverable		1,493,267
Reinsurance balances receivable		299,579
Ceded unearned premiums		1,143,852
Deferred acquisition costs and value of business acquired		679,259
Intangible assets		988,000
Other assets		314,168
Total assets		16,516,563
LIABILITIES
Unpaid losses and loss expenses		6,933,144
Unearned premiums		3,742,234
Reinsurance balances payable		1,441,749
Notes payable and debt		82,066
Payable for investments purchased		34,149
Deferred tax liability		94,071
Other liabilities		265,728
Total liabilities		12,593,141
Net assets acquired before non-controlling interest		3,923,422
Non-controlling interest in equity of consolidated subsidiaries		562,285
Net assets acquired		3,361,137
Acquisition consideration		4,139,180
Goodwill		778,043
Catlin Group Limited | Accrued investment income
ASSETS
Receivables acquired		35,063
Catlin Group Limited | Premiums receivable
ASSETS
Receivables acquired		2,545,188
Catlin Group Limited | Receivable from investments sold
ASSETS
Receivables acquired		$ 9,633

[1] Includes Restricted Cash