Schedule IV. Supplemental Schedule of Reinsurance Premiums (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Supplemental Schedule of Reinsurance Premiums for Insurance Companies [Abstract]
Gross Amounts									$ 157,112	$ 98,182	$ 66,027
Ceded									628,675	466,719	453,658
Assumed									1,874,993	1,769,088	1,450,047
Net premiums earned	$ 351,901	$ 346,521	$ 351,402	$ 353,606	$ 361,575	$ 362,388	$ 379,828	$ 296,760	$ 1,403,430	$ 1,400,551	$ 1,062,416
Percentage of Amount Assumed to Net									134.00%	126.00%	136.00%