Reinsurance - Components of Unpaid Losses and Loss Expenses Recoverable (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Analysis of total unpaid losses and loss expenses recoverable by segment:
Unpaid losses and loss expenses recoverable	$ 5,262,706	$ 3,429,368
Total P And C Segment [Member]
Analysis of total unpaid losses and loss expenses recoverable by segment:
Unpaid losses and loss expenses recoverable	5,248,905	3,411,528
Corporate and other
Analysis of total unpaid losses and loss expenses recoverable by segment:
Unpaid losses and loss expenses recoverable	$ 13,801	$ 17,840