Investments (Allowance for Credit Losses and Recorded Investment in Commercial Mortgage and Other Loans) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012		Dec. 31, 2011
Allowance for Credit Losses:
Ending Balance: Individually evaluated for impairment	$ 0	[1]	$ 0	[1]
Ending Balance: collectively evaluated for impairment	2,177	[2]	1,501	[2]
Total	2,177		1,501
Recorded Investment:
Ending balance gross of reserves: individually evaluated for impairment	0	[1],[3]	0	[1],[3]
Ending balance gross of reserves: collectively evaluated for impairment	429,158	[2],[3]	450,860	[2],[3]
Total	429,158	[3]	450,860	[3]
Agricultural Property Loans [Member]
Allowance for Credit Losses:
Ending Balance: collectively evaluated for impairment	200		200
Recorded Investment:
Ending balance gross of reserves: collectively evaluated for impairment	$ 50,000		$ 49,000

[1] There were no agricultural loans individually evaluated for impairments at December 31, 2012 and 2011.

[2] Agricultural loans collectively evaluated for impairment had a recorded investment of $50 million and $49 million at December 31, 2012 and 2011, respectively, and a related allowance of $0.2 million for both periods.

[3] Recorded investment reflects the balance sheet carrying value gross of related allowance.