Fair Value Measurements (Details 3)	12 Months Ended
	Dec. 31, 2011
Fair Value Measurement (Textual) [Abstract]
Maximum number of months related to maturities in the portfolio not to exceeded from the date of purchase	13 months
Maximum number of days related to dollar-weighted average portfolio maturities regarding commingled funds	90 days
Maximum maturity for longer term investment grade fixed income obligations (in years)	5 years
Minimum number of months related to the reset date of maturities in the portfolio with put features or floating rates	13 months