Derivative Instruments (Details 3) (Interest Rate Swaps, USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Derivatives In Cash Flow Hedging Relationships [Line Items]
Gains Losses Deferred In Accumulated Other Comprehensive Income Loss On Derivatives Effective Portion	$ (6,797)	$ 464	$ (4,934)	$ 787
Investment Related Gains (Losses)
Derivatives In Cash Flow Hedging Relationships [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	0	0	0	0
Derivative Instruments, Gain (Loss) Recognized in Income, Ineffective Portion and Amount Excluded from Effectiveness Testing, Net	31	27	14	3
Investment Income
Derivatives In Cash Flow Hedging Relationships [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	201	321	506	678
Derivative Instruments, Gain (Loss) Recognized in Income, Ineffective Portion and Amount Excluded from Effectiveness Testing, Net	$ 0	$ 0	$ 0	$ 0