Investments (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 263,899,000	$ 51,773,000
Gross unrealized gains	294,000	60,000
Gross unrealized losses	(393,000)	(1,021,000)
Fair market value	263,800,000	50,812,000
Loss on long-term investments	2,562,000	0	0
Federal agency notes [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	124,682,000	18,759,000
Gross unrealized gains	33,000	0
Gross unrealized losses	0	(138,000)
Fair market value	124,715,000	18,621,000
Commercial paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	137,661,000	31,795,000
Gross unrealized gains	0	0
Gross unrealized losses	(393,000)	(883,000)
Fair market value	137,268,000	30,912,000
Other Noncurrent Assets [Member]
Schedule of Available-for-sale Securities [Line Items]
Long-term Investments	2,900,000
Other Noncurrent Assets [Member] | Mutual funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,556,000	1,219,000
Gross unrealized gains	261,000	60,000
Gross unrealized losses	0	0
Fair market value	$ 1,817,000	$ 1,279,000