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, 2016	Dec. 31, 2015
Deferred tax assets:
Loss and LAE reserves	$ 212,100	$ 242,700
Minimum tax credit carry forward	28,900	110,200
Compensation accruals	166,700	161,900
Unearned premiums	139,100	134,000
OTTI losses	19,500	21,900
State net operating loss carry forward	25,200	17,900
Other	173,300	167,200
Gross deferred tax assets before valuation allowance	764,800	855,800
Valuation allowance	(25,200)	(17,900)
Gross deferred tax assets	739,600	837,900
Deferred tax liabilities:
Net unrealized gains on investments	125,800	120,800
Deferred acquisition costs	163,300	146,800
Purchase accounting adjustments	30,200	43,800
Other	65,400	58,100
Gross deferred tax liabilities	384,700	369,500
Net deferred tax assets	$ 354,852	$ 468,440