Cash and Cash Equivalents and Short-term Investments (Details 3) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014
Gross unrealized losses of cash and cash equivalents and short-term investments
Available-for-sale securities, more than 12 months	$ 18
Available-for-sale securities, continuous unrealized loss position, 12 months or longer, aggregate losses	1
Debt Securities
Gross unrealized losses of cash and cash equivalents and short-term investments
Available-for-sale securities, more than 12 months	18
Available-for-sale securities, continuous unrealized loss position, 12 months or longer, aggregate losses	1
Collateralized Debt Obligations
Gross unrealized losses of cash and cash equivalents and short-term investments
Available-for-sale securities, more than 12 months	18
Available-for-sale securities, continuous unrealized loss position, 12 months or longer, aggregate losses	$ 1