Investment Securities - Schedule of Amortized Cost and Estimated Fair Value of Fixed-Maturity Securities by Contractual Maturity (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Maturity in:
Amortized Cost, 2013	$ 82,371
Amortized Cost, 2014-2017	99,575
Amortized Cost, 2018-2022	39,888
Amortized Cost, Thereafter	40,520
Mortgage-backed securities, Amortized Cost	10,541
Total fixed-maturity securities, Amortized Cost	272,895	298,978
Estimated Fair Value, 2013	82,577
Estimated Fair Value, 2014-2017	103,196
Estimated Fair Value, 2018-2022	40,136
Estimated Fair Value, Thereafter	41,042
Mortgage-backed securities, Estimated Fair Value	10,518
Total fixed-maturity securities, Estimated Fair Value	$ 277,469	$ 304,045