Schedule VI - Supplementary Information Concerning Property/Casualty Insurance Operations (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Supplemental Information for Property, Casualty Insurance Underwriters [Line Items]
Deferred Acquisition Costs	$ 89,123				$ 61,706				$ 89,123	$ 61,706	$ 16,744
Reserves for Unpaid Losses and Loss Adjustment Expenses	5,720,149				4,509,421				5,720,149	4,509,421	4,219,905
Unearned Premiums	542,661				467,933				542,661	467,933	67,003
Net Premiums Earned									752,190	540,746	144,823
Net Investment Income(1)									102,347	64,968	62,411
Net Losses and Loss Expenses Incurred - Current Year									476,364	327,817	93,442
Net Loses and Loss Expenses Incurred - Prior Year									(372,031)	(318,671)	(257,114)
Net Paid Losses and Loss Expenses									(781,889)	(587,511)	401,496
Amortization of Deferred Acquisition Costs									163,716	117,544	14,379
Net Premiums Written									785,601	545,721	39,337
Net investment income	51,599	$ 40,286	$ 34,779	$ 30,990	24,889	$ 25,706	$ 26,485	$ 24,326	157,654	101,406	89,920
Other income	$ 20,519	$ 2,883	$ 11,714	$ 2,903	$ 6,499	$ 2,278	$ 7,164	$ 22	$ 38,019	15,963	3,375
Scenario, Previously Reported
Supplemental Information for Property, Casualty Insurance Underwriters [Line Items]
Net investment income										14,100	2,200
Scenario, Adjustment
Supplemental Information for Property, Casualty Insurance Underwriters [Line Items]
Other income										$ 14,100	$ 2,200