Fair Value Measurements (Details 4) (Level 3, Recurring, Corporate debt, Discounted cash flows)	9 Months Ended	12 Months Ended
	Sep. 30, 2013	Dec. 31, 2012
Minimum
Unobservable Input
Yield (as a percent)	2.61%	2.74%
Maximum
Unobservable Input
Yield (as a percent)	7.61%	7.35%
Weighted Average
Unobservable Input
Yield (as a percent)	4.41%	4.45%