Fair Value Measurement (Narrative) (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2013 transfers	Jun. 30, 2012 transfers	Jun. 30, 2013 Minimum [Member] broker	Jun. 30, 2013 Commercial Mortgage Backed Securities [Member] Level 2 [Member]	Dec. 31, 2012 Commercial Mortgage Backed Securities [Member] Level 2 [Member]
Fair Value Measurement [Line Items]
Percentage of portfolio of unadjusted fair values obtained	98.00%
Percentage of portfolio of specific unadjusted broker quotes obtained	2.00%
Number of knowledgeable outside security brokers consulted to determine fair value			1
Trading securities, fair value disclosure				$ 12.4	$ 4.3
Transfers between Levels 1, 2, and 3 of the fair value hierarchy	0	0