Cash and Cash Equivalents and Short-term Investments (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012	Dec. 31, 2011
Cash and Cash Equivalents and Short-term Investments
Cash and cash equivalents	$ 395,923	$ 524,922	$ 471,562	$ 398,575
Short-term investments:
Trading equity securities		52,705
Available-for-sale equity securities	76,469	174,610
Available-for-sale debt securities	19,546	25,967
Total short-term investments	$ 96,015	$ 253,282