Investment Securities - Schedule of Amortized Cost and Estimated Fair Value of Fixed-Maturity Securities by Contractual Maturity (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Maturity in:
Amortized Cost, 2013	$ 62,361
Amortized Cost, 2014-2017	130,860
Amortized Cost, 2018-2022	30,677
Amortized Cost, Thereafter	23,333
Mortgage-backed securities, Amortized Cost	2,385
Total fixed-maturity securities, Amortized Cost	249,616	272,895
Estimated Fair Value, 2013	62,356
Estimated Fair Value, 2014-2017	132,576
Estimated Fair Value, 2018-2022	29,964
Estimated Fair Value, Thereafter	23,072
Mortgage-backed securities, Estimated Fair Value	2,332
Total fixed-maturity securities, Estimated Fair Value	$ 250,300	$ 277,469