Investments - Summary of Amortized Cost and Fair Value of Investments in Fixed Maturity Securities by Contractual Maturity (Total Available-for-sale Securities) (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Investment [Line Items]
Less than one year, Amortized Cost Basis	$ 28,681
One to five years, Amortized Cost Basis	28,734
Five to ten years, Amortized Cost Basis	18,162
More than ten years, Amortized Cost Basis	121,538
Total, Amortized Cost Basis	207,197	144,514
Less than one year, Fair Value	28,802
One to five years, Fair Value	28,993
Five to ten years, Fair Value	18,357
More than ten years, Fair Value	118,508
Total, Fair Value	202,701	149,139
U.S. agency-based mortgage-backed securities [Member]
Investment [Line Items]
U.S. agency-based mortgage-backed securities, Amortized Cost Basis	10,082
U.S. agency-based mortgage-backed securities, Fair Value	$ 8,041