Cash and Cash Equivalents and Short-term Investments (Details 2) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Sep. 30, 2013
Cash and cash equivalents and short-term investments
Cash and cash equivalents, fair value	$ 524,922	$ 395,923
Short-term investments:
Trading equity securities, fair value	52,705
Trading equity securities, gross unrealized holding gains	46,981
Available-for-sale equities securities
Available-for-sale equity securities, fair value	200,577	96,015
Available-for-sale debt securities:
Total available-for-sale debt securities, fair value	25,967	19,546
Available-for-sale securities, gross unrealized holding gains	139,205	51,124
Available-for-sale securities, gross unrealized holding losses	(1,225)	(69)
Total short-term investments	253,282	96,015
Total cash, cash equivalents and short-term investments, fair value	778,204	491,938
Total cash, cash equivalents and short-term investments, gross unrealized gains	186,186	51,124
Total cash, cash equivalents and short-term investments, gross unrealized losses	(1,225)	(69)
Available-for-sale equity securities
Available-for-sale equities securities
Available-for-sale equity securities, fair value	174,610	76,469
Available-for-sale debt securities:
Available-for-sale securities, gross unrealized holding gains	137,282	47,922
Available-for-sale securities, gross unrealized holding losses	(1,030)
Available-for-sale debt securities
Available-for-sale debt securities:
Total available-for-sale debt securities, fair value	25,967	19,546
Available-for-sale securities, gross unrealized holding gains	1,923	3,202
Available-for-sale securities, gross unrealized holding losses	(195)	(69)
Commercial paper and CDs
Available-for-sale debt securities:
Total available-for-sale debt securities, fair value	206
Corporate debt securities
Available-for-sale debt securities:
Total available-for-sale debt securities, fair value	23,399	18,448
Available-for-sale securities, gross unrealized holding gains	1,870	3,188
Mortgage-backed debt securities
Available-for-sale debt securities:
Total available-for-sale debt securities, fair value	244	213
Available-for-sale securities, gross unrealized holding gains	15	12
Mortgage-CMO debt securities
Available-for-sale debt securities:
Total available-for-sale debt securities, fair value	523	60
Available-for-sale securities, gross unrealized holding gains	10	2
Available-for-sale securities, gross unrealized holding losses	(3)	(2)
Asset-backed debt securities
Available-for-sale debt securities:
Total available-for-sale debt securities, fair value	1,595	825
Available-for-sale securities, gross unrealized holding gains	28
Available-for-sale securities, gross unrealized holding losses	(192)	(67)
Total Short-term investments
Available-for-sale debt securities:
Total short-term investments	253,282	96,015
Total short-term investments, gross unrealized gains	186,186	51,124
Total short-term investments, gross unrealized holding losses	$ (1,225)	$ (69)