Cash and Cash Equivalents and Short-term Investments (Details 5) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Available-for-sale:
Proceeds from sales and maturities	$ 408	$ 3,953	$ 107,361	$ 23,186
Realized gains (losses), net	$ 2	$ 1,732	$ 88,159	$ 14,007