SCHEDULE VI - Supplemental Information Concerning Property-Casualty Insurance Operations (Details) (Consolidated subsidiaries [Member], USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Consolidated subsidiaries [Member]
Supplemental Information Concerning Property-Casualty Insurance Operations [Line Items]
Deferred policy acquisition costs	$ 463,958	$ 434,111	$ 363,188
Liability for unpaid losses and loss expenses	9,745,806	10,646,318	10,709,371
Unearned premiums	1,731,212	1,699,430	1,517,358
Premiums earned	4,387,444	4,241,064	3,691,341
Losses and loss expenses incurred	2,462,568	2,397,256	2,157,629
Amortization of deferred policy acquisition costs	1,065,133	952,997	821,022
Paid losses and loss expenses	2,798,549	2,401,559	2,705,062
Premiums written	$ 4,500,214	$ 4,432,829	$ 3,774,474