Investments - Summary of the Amortized Cost and Fair Value of Investments in Fixed Maturity Securities, Classified as Held-to-maturity (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Investment [Line Items]
Due in 2014, Amortized Cost	$ 55,379
In 2015 through 2018, Amortized Cost	139,890
In 2019 through 2023, Amortized Cost	134,404
After 2023, Amortized Cost	130,938
Total, Amortized Cost	536,583	583,287
Due in 2014, Fair Value	55,758
In 2015 through 2018, Fair Value	147,515
In 2019 through 2023, Fair Value	143,566
After 2023, Fair Value	133,075
Total, Fair Value	561,179	627,349
U.S. agency-based mortgage-backed securities [Member]
Investment [Line Items]
Held-to-maturity, Amortized Cost	21,775
Held-to-maturity, Fair Value	23,565
Commercial mortgage-backed securities [Member]
Investment [Line Items]
Held-to-maturity, Amortized Cost	50,813
Held-to-maturity, Fair Value	54,244
Asset-backed securities [Member]
Investment [Line Items]
Held-to-maturity, Amortized Cost	3,384
Held-to-maturity, Fair Value	$ 3,456