Supplementary Information for Property Casualty Underwriters (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Supplemental Information for Property, Casualty Insurance Underwriters [Line Items]
Deferred Policy Acquisition Costs	$ 57,901	$ 56,517	$ 25,238
Reserves for Unpaid Claims and Claim Adjustment Expenses	651,042	680,047	675,472
Discount If Any Deducted	2,000	3,000	4,000
Unearned Premiums	286,984	286,285	120,815
Earned Premiums	468,465	504,143	268,519
Net Investment Income	33,983	34,609	28,821
Claims and Claim Adjustment Expense Incurred Related To Current Year	321,255	310,066	153,994
Claims and Claim Adjustment Expense Incurred Related To Prior Year	(57,252)	(34,698)	(16,433)
Amortization Of Deferred Policy Acquisition Costs	114,317	86,170	57,051
Paid Claims and Claim Adjustment Expenses	317,369	332,417	172,265
Premiums Written	$ 470,940	$ 501,244	$ 273,181