Investment Securities - Schedule of Amortized Cost and Estimated Fair Value of Fixed-Maturity Securities by Contractual Maturity (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Maturity in:
Amortized Cost, 2013	$ 89,942
Amortized Cost, 2014-2017	106,563
Amortized Cost, 2018-2022	43,180
Amortized Cost, Thereafter	29,076
Mortgage-backed securities, Amortized Cost	8,893
Total fixed-maturity securities, Amortized Cost	277,654	272,895
Estimated Fair Value, 2013	90,034
Estimated Fair Value, 2014-2017	109,789
Estimated Fair Value, 2018-2022	43,405
Estimated Fair Value, Thereafter	29,471
Mortgage-backed securities, Estimated Fair Value	8,848
Total fixed-maturity securities, Estimated Fair Value	$ 281,547	$ 277,469