Fair Value Measurements (Details 4) (Level 3, Recurring, Corporate debt, Discounted cash flows)	3 Months Ended	12 Months Ended
	Mar. 31, 2013	Dec. 31, 2012
Minimum
Unobservable Input
Yield (as a percent)	2.67%	2.74%
Maximum
Unobservable Input
Yield (as a percent)	7.35%	7.35%
Weighted Average
Unobservable Input
Yield (as a percent)	4.38%	4.45%