Investments - Additional Information (Detail) $ in Thousands	3 Months Ended			12 Months Ended
	Jun. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Dec. 31, 2016 USD ($) Security	Dec. 31, 2015 USD ($) Security	Dec. 31, 2014 USD ($)
Schedule of Investments [Line Items]
Other invested assets				$ 1,960
Non-credit OTTI on fixed maturities in a net unrealized net gain position				400	$ 500
Gross Unrealized Loss				30,199	29,398
OTTI losses	$ 150	$ 1,275	$ 423	$ 150	$ 1,698	$ 0
Equity Securities
Schedule of Investments [Line Items]
Number of securities in unrealized loss position | Security				75	57
Gross Unrealized Loss				$ 5,785	$ 3,013
Fixed maturities
Schedule of Investments [Line Items]
Number of securities in unrealized loss position | Security				413	368
Gross Unrealized Loss				$ 24,414	$ 26,385
OTTI losses				200
Equity Portfolio
Schedule of Investments [Line Items]
OTTI losses					1,700
Non-government-backed securities
Schedule of Investments [Line Items]
Gross Unrealized Loss				$ 1,000	$ 2,600
Non-government-backed securities | Maximum
Schedule of Investments [Line Items]
Percentage of investment				5.00%	5.00%
Mortgage-backed and asset-backed securities
Schedule of Investments [Line Items]
Securities, effective maturities				4 years 10 months 24 days
Mortgage-backed and asset-backed securities | Fixed maturities
Schedule of Investments [Line Items]
Gross Unrealized Loss				$ 9,722	$ 5,652