Investments (Details 3) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Continuous unrealized loss position, Fair Value
Fair Value, Total	$ 81,711	$ 245,320
Continuous unrealized loss position, Gross Unrealized Loss
Gross Unrealized Loss, Total	(84)	(240)
US Government-sponsored Enterprises Debt Securities [Member]
Continuous unrealized loss position, Fair Value
Less than one year, Fair value	13,747	76,651
Fair Value, Total	13,747	76,651
Continuous unrealized loss position, Gross Unrealized Loss
Less than one year, Gross Unrealized Loss	(18)	(77)
Gross Unrealized Loss, Total	(18)	(77)
Corporate Debt Securities [Member]
Continuous unrealized loss position, Fair Value
Less than one year, Fair value	67,964	168,669
Fair Value, Total	67,964	168,669
Continuous unrealized loss position, Gross Unrealized Loss
Less than one year, Gross Unrealized Loss	(66)	(163)
Gross Unrealized Loss, Total	$ (66)	$ (163)