Cash and Cash Equivalents and Short-term Investments (Details 4) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Available-for-sale:
Proceeds from sales and maturities	$ 22,178	$ 20,352	$ 22,313	$ 106,953
Realized gains (losses), net	$ 4,903	$ 12,183	$ 4,903	$ 88,157