Reinsurance (List of Direct, Assumed, and Ceded Reinsurance Amounts) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Premiums written:
Direct	$ 631,429	$ 592,858	$ 1,851,620	$ 1,723,063
Assumed	6,099	5,780	17,140	19,467
Ceded premiums written	(92,503)	(103,517)	(273,514)	(290,836)
Net	545,025	495,121	1,595,246	1,451,694
Premiums earned:
Direct	590,716	548,734	1,728,865	1,630,347
Assumed	5,830	6,789	16,831	27,359
Ceded premiums earned	(89,156)	(92,884)	(271,874)	(274,947)
Net	507,390	462,639	1,473,822	1,382,759
Loss and loss expense incurred:
Direct	306,635	304,525	935,529	995,581
Assumed	4,224	5,362	13,114	20,218
Ceded loss and loss expense incurred	(25,698)	(38,955)	(86,922)	(126,526)
Net	285,161	270,932	861,721	889,273
National Flood Insurance Program [Member]
Premiums written:
Ceded premiums written	(62,463)	(69,922)	(178,784)	(193,000)
Premiums earned:
Ceded premiums earned	(58,340)	(60,761)	(176,119)	(178,260)
Loss and loss expense incurred:
Ceded loss and loss expense incurred	$ (15,382)	$ (14,008)	$ (36,315)	$ (48,099)