Cash, Cash Equivalents and Investments (Details 3) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011
Effective maturity dates of available-for-sale investments
Less than 1 Year	$ 144,431
1-2 Years	82,500
2-3 Years	56,087
3-4 Years	2,398
4-5 Years	27,988
Fair Value, Total	313,404
Treasury bills [Member]
Effective maturity dates of available-for-sale investments
Less than 1 Year	1,945
1-2 Years	0
2-3 Years	0
3-4 Years	0
4-5 Years	0
Fair Value, Total	1,945
Municipal bonds [Member]
Effective maturity dates of available-for-sale investments
Less than 1 Year	54,036
1-2 Years	25,713
2-3 Years	23,976
3-4 Years	0
4-5 Years	19,991
Fair Value, Total	123,716
Corporate bonds [Member]
Effective maturity dates of available-for-sale investments
Less than 1 Year	55,570
1-2 Years	33,555
2-3 Years	21,543
3-4 Years	2,398
4-5 Years	2,406
Fair Value, Total	115,472
Agency bonds [Member]
Effective maturity dates of available-for-sale investments
Less than 1 Year	27,545
1-2 Years	7,700
2-3 Years	4,635
3-4 Years	0
4-5 Years	0
Fair Value, Total	39,880
Sovereign bonds [Member]
Effective maturity dates of available-for-sale investments
Less than 1 Year	4,016
1-2 Years	10,831
2-3 Years	5,933
3-4 Years	0
4-5 Years	5,591
Fair Value, Total	26,371
Covered bonds [Member]
Effective maturity dates of available-for-sale investments
Less than 1 Year	1,319
1-2 Years	4,701
2-3 Years	0
3-4 Years	0
4-5 Years	0
Fair Value, Total	$ 6,020