Investments - Additional Information (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($) Security	Dec. 31, 2017 USD ($) Security	Dec. 31, 2016 USD ($)
Schedule of Investments [Line Items]
Non-credit OTTI on fixed maturities in a net unrealized gain position	$ 300	$ 500
Fixed Maturities
Schedule of Investments [Line Items]
Number of securities in unrealized loss position | Security	808	454
Gross Unrealized Loss	$ 60,549	$ 14,512
OTTI losses			$ 200
Equity Securities
Schedule of Investments [Line Items]
Number of securities in unrealized loss position | Security		22
OTTI losses		$ 2,100
Mortgage-Backed and Asset-Backed Securities
Schedule of Investments [Line Items]
Securities, effective maturities	5 years 2 months 12 days
Mortgage-Backed and Asset-Backed Securities | Fixed Maturities
Schedule of Investments [Line Items]
Gross Unrealized Loss	$ 24,504	$ 7,338
Maximum | Non-government-backed securities
Schedule of Investments [Line Items]
Percentage of investment	5.00%	5.00%
Gross Unrealized Loss	$ 3,700	$ 700
Other Invested Assets
Schedule of Investments [Line Items]
Equity method investments, cost	2,000
Equity method investments, carrying Value	1,900	1,700
Fair value of overseas deposits	$ 46,500	$ 28,800