Schedule VI. Supplementary Insurance Information Concerning Property-Casualty Insurance Operations (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Supplemental Information for Property, Casualty Insurance Underwriters [Line Items]
Current year	$ 694,957	$ 610,685	$ 341,745
Prior years	(164,126)	(162,447)	(143,798)
Consolidated Subsidiaries
Supplemental Information for Property, Casualty Insurance Underwriters [Line Items]
Deferred Policy Acquisition Costs	335,325	199,380	110,059
Reserves for Unpaid Claims and Claim Adjustment Expenses	2,848,294	2,767,045	1,412,510
Discount, if any, Deducted	0	0	0
Unearned Premiums	1,231,573	889,102	512,386
Earned Premiums	1,403,430	1,400,551	1,062,416
Net Investment Income	181,726	152,567	124,316
Current year	694,957	610,685	341,745
Prior years	(164,126)	(162,447)	(143,798)
Amortization of Deferred Policy Acquisition Costs	289,323	238,592	144,476
Paid Claims and Claims Adjustment Expenses	589,294	521,312	281,116
Net Premiums Written	$ 1,535,312	$ 1,416,183	$ 1,068,236