Current Marketable Securities Maturity Periods for Investments (Details)	9 Months Ended
	Sep. 30, 2013
Corporate bonds | Minimum
Schedule of Available-for-sale Securities [Line Items]
Investment maturity period	1 year
Corporate bonds | Maximum
Schedule of Available-for-sale Securities [Line Items]
Investment maturity period	5 years
US Government Agencies Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Investment maturity period	1 year
Mortgage-backed securities | Minimum
Schedule of Available-for-sale Securities [Line Items]
Investment maturity period	4 years
Mortgage-backed securities | Maximum
Schedule of Available-for-sale Securities [Line Items]
Investment maturity period	26 years
Asset-backed securities | Minimum
Schedule of Available-for-sale Securities [Line Items]
Investment maturity period	2 years
Asset-backed securities | Maximum
Schedule of Available-for-sale Securities [Line Items]
Investment maturity period	5 years