Investment Securities - Schedule of Amortized Cost and Estimated Fair Value of Fixed-Maturity Securities by Contractual Maturity (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Maturity in:
Amortized Cost, 2013	$ 73,418
Amortized Cost, 2014-2017	124,916
Amortized Cost, 2018-2022	42,272
Amortized Cost, Thereafter	26,681
Mortgage-backed securities, Amortized Cost	3,469
Total fixed-maturity securities, Amortized Cost	270,486	272,895
Estimated Fair Value, 2013	73,167
Estimated Fair Value, 2014-2017	126,578
Estimated Fair Value, 2018-2022	40,983
Estimated Fair Value, Thereafter	26,475
Mortgage-backed securities, Estimated Fair Value	3,401
Total fixed-maturity securities, Estimated Fair Value	$ 270,604	$ 281,547