Income Taxation - Components of Deferred Tax Assets and Deferred Tax Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Deferred tax assets:
Net operating loss carryforwards	$ 159,436	$ 183,633
Insurance reserves	14,104	18,677
Unearned premiums	7,131	11,314
Lloyd's underwriting losses taxable in future periods	0	6,201
Provisions for bad debt	6,172	2,594
Unrealized losses on investments	0	5,160
Defendant asbestos and environmental liabilities	140,000	0
Other deferred tax assets	0	183
Gross deferred tax assets	326,843	227,762
Valuation allowance	(117,390)	(212,113)
Deferred tax assets	209,453	15,649
Deferred tax liabilities:
Unrealized gains on investments	(10,107)	0
Lloyd's underwriting profit taxable in future periods	(8,852)	0
Deferred policy acquisition cost	(8,267)	0
Other deferred tax liabilities	(27,317)	(16,067)
Deferred tax liabilities	(54,543)	(16,067)
Net deferred tax asset	$ 154,910
Net deferred tax liability		$ (418)