Summary of Significant Accounting Policies - Additional Information (Detail) $ in Thousands		9 Months Ended	12 Months Ended
		Sep. 30, 2018 USD ($) Country State	Dec. 31, 2018	Dec. 31, 2017 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Number of countries in which company operates | Country		20
Number of states in which company licensed to sell insurance and annuities | State		49
Net increase correction of prior period error		$ 4,500
Accumulated Other Comprehensive Income
Summary Of Significant Accounting Policies [Line Items]
Cumulative effect adjustment	[1],[2]			$ (3,023)
Retained Earnings (Deficit)
Summary Of Significant Accounting Policies [Line Items]
Cumulative effect adjustment	[2]			$ 3,023
Minimum | Scenario, Forecast
Summary Of Significant Accounting Policies [Line Items]
Interest rates for future policy benefits liabilities			0.01%
Maximum | Scenario, Forecast
Summary Of Significant Accounting Policies [Line Items]
Interest rates for future policy benefits liabilities			9.60%

[1] See Notes to Financial Statements – Note 1, Summary of Significant Accounting Policies, Current Accounting Guidance, for discussion on the adjustment relating to ASU 2016-01.

[2] See Notes to Financial Statements – Note 1, Summary of Significant Accounting Policies, Current Accounting Guidance, for discussion on the adjustment relating to Accounting Standards Update (“ASU”) 2016-01.