Investments - Additional Information (Detail) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2016 USD ($) Security	Mar. 31, 2015 USD ($)	Dec. 31, 2015 USD ($) Security
Schedule of Investments [Line Items]
Non-credit OTTI on fixed maturities in an unrealized gain position	$ 400		$ 500
Gross Unrealized Loss	17,963		$ 29,398
OTTI losses	0	$ 0
Credit loss portion of the OTTI losses on fixed maturities	$ 2,400	$ 2,400
Equity Securities
Schedule of Investments [Line Items]
Number of securities in unrealized loss position | Security	36		57
Gross Unrealized Loss	$ 1,646		$ 3,013
Fixed maturities
Schedule of Investments [Line Items]
Number of securities in unrealized loss position | Security	204		368
Gross Unrealized Loss	$ 16,317		$ 26,385
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	$ 2,300		$ 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 1 month 6 days
Mortgage-backed and asset-backed securities | Fixed maturities
Schedule of Investments [Line Items]
Gross Unrealized Loss	$ 4,212		$ 5,652