Tax Effects of Temporary Differences that Give Rise to Significant Portions of Deferred Tax Assets and Deferred Tax Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Deferred tax assets:
Loss and LAE reserves	$ 118,900	$ 122,900
Minimum tax credit carry forward		68,800
Compensation accruals	94,100	88,100
Unearned premiums	97,400	85,900
OTTI losses	6,500	5,400
State net operating loss carry forward	22,800	23,500
Other	134,900	89,800
Gross deferred tax assets before valuation allowance	474,600	484,400
Valuation allowance	(22,800)	(23,500)
Gross deferred tax assets	451,800	460,900
Deferred tax liabilities:
Net unrealized gains on investments	274,800	127,200
Deferred acquisition costs	113,400	101,100
Purchase accounting adjustments	11,700	11,300
Other	46,000	56,400
Gross deferred tax liabilities	445,900	296,000
Net deferred tax assets	$ 5,860	$ 164,890