Derivative Instruments (Exposure from Credit Derivatives by NAIC Rating of the Underlying Credits) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Credit Derivatives [Line Items]
Notional	$ 0	$ 315,000
Aggregate fair value of all derivative instruments with credit-risk-related contingent features in a net liability position	$ 0	$ 411