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Investments - Additional Information (Detail)
 3 Months Ended 9 Months Ended
Sep. 30, 2016
USD ($)
Security
Sep. 30, 2015
USD ($)
Sep. 30, 2016
USD ($)
Security
Sep. 30, 2015
USD ($)
Security
Investments Schedule [Abstract]        
Individual fixed maturity held in unrealized loss position | Security 73   73  
Individual fixed maturity held in unrealized loss position longer than 12 months | Security 19   19  
Carrying value of investments $ 12,200,000   $ 12,200,000  
Impairment losses recognized     0 $ 2,700,000
Net realized gains (losses) on investments $ 181,000 $ 40,000 $ 974,000 $ (2,518,000)
Number of fixed maturity securities to be deemed other-than-temporarily impaired | Security       4
Net realized gain(loss)outside OTTI       $ 200,000