Income Taxes - Components of Deferred Tax Assets (Liabilities) (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Deferred tax assets:
Unearned premiums	$ 10,780	$ 12,488
Unearned commission	10,417	11,987
Net operating loss		4,727
Tax-related discount on loss reserve	1,486	1,250
Unrealized loss	3,347
Stock-based compensation	1,126
Prepaid expenses	2,214	1,950
Other	1,429	331
Total deferred tax asset	30,799	32,733
Deferred tax liabilities:
Deferred acquisition costs	18,216	9,775
Prepaid expenses	342	27,568
Unrealized gains		30
Property and equipment	452
Note discount	2,498	3,818
Basis in purchased investments	179	335
Basis in purchased intangibles	19,518	24,250
Other	1,557	1,290
Total deferred tax liabilities	42,762	67,066
Net deferred tax liability	$ (11,963)	$ (34,333)