Investments (Details 2) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012
Cost or Amortized cost [Member]
Summary of the cost or amortized cost and fair value of investments in fixed maturity securities, classified as held-to-maturity, by contractual maturity
Due in 2013	$ 81,159
In 2014 through 2017	147,800
In 2018 through 2022	138,680
After 2022	126,906
Total, Amortized cost	583,287
Fair Value [Member]
Summary of the cost or amortized cost and fair value of investments in fixed maturity securities, classified as held-to-maturity, by contractual maturity
Due in 2013, Fair value	81,897
In 2014 through 2017, Fair value	156,272
In 2018 through 2022, Fair value	154,343
After 2022, Fair value	136,588
Total, Fair Value	627,349
U.S. agency-based mortgage-backed securities [Member] | Cost or Amortized cost [Member]
Summary of the cost or amortized cost and fair value of investments in fixed maturity securities, classified as held-to-maturity, by contractual maturity
Held-to-maturity, Amortized cost	32,984
U.S. agency-based mortgage-backed securities [Member] | Fair Value [Member]
Summary of the cost or amortized cost and fair value of investments in fixed maturity securities, classified as held-to-maturity, by contractual maturity
Held-to-maturity, Fair Value	36,042
Commercial mortgage-backed securities [Member] | Cost or Amortized cost [Member]
Summary of the cost or amortized cost and fair value of investments in fixed maturity securities, classified as held-to-maturity, by contractual maturity
Held-to-maturity, Amortized cost	51,529
Commercial mortgage-backed securities [Member] | Fair Value [Member]
Summary of the cost or amortized cost and fair value of investments in fixed maturity securities, classified as held-to-maturity, by contractual maturity
Held-to-maturity, Fair Value	57,962
Asset-backed securities [Member] | Cost or Amortized cost [Member]
Summary of the cost or amortized cost and fair value of investments in fixed maturity securities, classified as held-to-maturity, by contractual maturity
Held-to-maturity, Amortized cost	4,229
Asset-backed securities [Member] | Fair Value [Member]
Summary of the cost or amortized cost and fair value of investments in fixed maturity securities, classified as held-to-maturity, by contractual maturity
Held-to-maturity, Fair Value	$ 4,245