Investments - Additional Information (Detail) $ in Thousands	3 Months Ended		12 Months Ended
	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Dec. 31, 2015 USD ($) Security	Dec. 31, 2014 USD ($) Security	Dec. 31, 2013 USD ($)
Schedule of Investments [Line Items]
Non-credit OTTI on fixed maturities in an unrealized gain position			$ 500	$ 700
Gross Unrealized Loss			29,398	11,651
OTTI losses	$ 1,275	$ 423	$ 1,698	$ 0	$ 2,393
Equity Securities And Municipal Bond
Schedule of Investments [Line Items]
OTTI losses					$ 2,400
Equity Securities
Schedule of Investments [Line Items]
Number of securities in unrealized loss position | Security			57	15
Gross Unrealized Loss			$ 3,013	$ 1,304
Fixed maturities
Schedule of Investments [Line Items]
Number of securities in unrealized loss position | Security			368	259
Gross Unrealized Loss			$ 26,385	$ 10,347
Maximum | Equity Securities
Schedule of Investments [Line Items]
Percentage of fair value under carrying value			80.00%
Non-government-backed securities
Schedule of Investments [Line Items]
Gross Unrealized Loss			$ 2,600	$ 500
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 7 months 6 days
Mortgage-backed and asset-backed securities | Fixed maturities
Schedule of Investments [Line Items]
Gross Unrealized Loss			$ 5,652	$ 2,198