Fair Value Measurement (Narrative) (Details) $ in Millions	3 Months Ended
	Mar. 31, 2016 USD ($) transfers broker	Mar. 31, 2015 transfers	Dec. 31, 2015 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Percentage of portfolio of unadjusted fair values obtained	99.70%
Percentage of portfolio of specific unadjusted broker quotes obtained	0.30%
Transfers between Levels 1, 2, and 3 of the fair value hierarchy | transfers	0	0
Commercial Mortgage Backed Securities [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities, fair value disclosure | $	$ 44.8		$ 37.3
Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Number of knowledgeable outside security brokers consulted to determine fair value | broker	1