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, 2020	Dec. 31, 2019
Deferred tax assets:
Loss and LAE reserves	$ 132,300	$ 118,900
Foreign tax credit carry forward	74,100	53,800
Compensation accruals	87,500	94,100
Unearned premiums	112,200	97,400
Allowance for credit losses on available for sale securities	5,700	6,500
State net operating loss carry forward	12,500	22,800
Other	98,000	113,700
Gross deferred tax assets before valuation allowance	522,300	507,200
Valuation allowance	(12,500)	(22,800)
Gross deferred tax assets	509,800	484,400
Deferred tax liabilities:
Net unrealized gains on investments	294,700	274,800
Deferred acquisition costs	128,400	113,400
Purchase accounting adjustments	11,700	11,700
Other	118,500	78,600
Gross deferred tax liabilities	553,300	478,500
Net deferred tax (liabilities)	(43,547)	0
Net deferred tax assets	$ 0	$ 5,860