Income Taxes - Components of Net Deferred Tax Asset (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Deferred federal income tax asset:
Net operating loss carryforward	$ 2,107,353	$ 2,104,944	$ 2,102,482
Change in net operating loss due to change in tax rates	(842,941)
Accruals and reserves	309	2,177	3,481
Derivative liability			19,117
Restricted stock grants	138	157	160
Net unrealized loss on investments	4	23	16
Capital loss carryforward	344	52,475	52,490
Total deferred federal income tax asset	1,265,207	2,159,776	2,177,746
Deferred federal income tax liabilities:
Losses and loss adjustments expense	304	500	411
Derivative asset		51,407
Total deferred federal income tax liabilities	304	51,907	411
Less: Valuation allowance	1,264,903	2,107,869	2,177,335
Net deferred federal income tax asset	$ 0	$ 0	$ 0