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Reinsurance (List of Direct, Assumed, and Ceded Reinsurance Amounts) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Premiums written:
Direct	$ 683,820	$ 646,278
Assumed	5,691	6,320
Ceded	(90,807)	(87,239)
Net	598,704	565,359
Premiums earned:
Direct	646,728	606,661
Assumed	5,779	6,270
Ceded	(91,653)	(90,473)
Net	560,854	522,458
Loss and loss expense incurred:
Direct	342,122	361,639
Assumed	4,437	6,355
Ceded	(29,087)	(70,850)
Net	317,472	297,144
National Flood Insurance Program [Member]
Premiums written:
Ceded	(56,334)	(53,248)
Premiums earned:
Ceded	(57,277)	(56,814)
Loss and loss expense incurred:
Ceded	$ (6,541)	$ (40,718)

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