Reinsurance - Components of Unpaid Losses and Loss Expenses Recoverable (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Analysis of total unpaid losses and loss expenses recoverable by segment:
Unpaid losses and loss expenses recoverable	$ 3,429,368	$ 3,435,230
Total P And C Segment [Member]
Analysis of total unpaid losses and loss expenses recoverable by segment:
Unpaid losses and loss expenses recoverable	3,411,526	3,414,735
Corporate and other
Analysis of total unpaid losses and loss expenses recoverable by segment:
Unpaid losses and loss expenses recoverable	$ 17,842	$ 20,495