Cash, Cash Equivalents and Investments (Details 1) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Summary of available-for-sale investments
Amortized Cost	$ 313,277
Gross Unrealized Gains	1,213
Gross Unrealized Losses	(1,086)
Fair Value, Short-term investments	144,431	147,823
Fair Value, Total	313,404
Treasury bills [Member]
Summary of available-for-sale investments
Fair Value, Short-term investments	1,945	2,494
Fair Value, Total	1,945
Treasury bills [Member] | Short-term investments [Member]
Summary of available-for-sale investments
Amortized Cost	1,944
Gross Unrealized Gains	1
Gross Unrealized Losses	0
Fair Value, Short-term investments	1,945
Municipal bonds [Member]
Summary of available-for-sale investments
Fair Value, Short-term investments	54,036	75,457
Fair Value, Long-term investments	69,680	34,794
Fair Value, Total	123,716
Municipal bonds [Member] | Short-term investments [Member]
Summary of available-for-sale investments
Amortized Cost	53,974
Gross Unrealized Gains	65
Gross Unrealized Losses	(3)
Fair Value, Short-term investments	54,036
Municipal bonds [Member] | Long-term investments [Member]
Summary of available-for-sale investments
Amortized Cost	69,576
Gross Unrealized Gains	201
Gross Unrealized Losses	(97)
Corporate bonds [Member]
Summary of available-for-sale investments
Fair Value, Short-term investments	55,570	34,543
Fair Value, Long-term investments	59,902	36,762
Fair Value, Total	115,472
Corporate bonds [Member] | Short-term investments [Member]
Summary of available-for-sale investments
Amortized Cost	56,277
Gross Unrealized Gains	32
Gross Unrealized Losses	(739)
Fair Value, Short-term investments	55,570
Corporate bonds [Member] | Long-term investments [Member]
Summary of available-for-sale investments
Amortized Cost	59,461
Gross Unrealized Gains	467
Gross Unrealized Losses	(26)
Agency bonds [Member]
Summary of available-for-sale investments
Fair Value, Short-term investments	27,545	15,979
Fair Value, Long-term investments	12,335	21,025
Fair Value, Total	39,880
Agency bonds [Member] | Short-term investments [Member]
Summary of available-for-sale investments
Amortized Cost	27,676
Gross Unrealized Gains	19
Gross Unrealized Losses	(150)
Fair Value, Short-term investments	27,545
Agency bonds [Member] | Long-term investments [Member]
Summary of available-for-sale investments
Amortized Cost	12,371
Gross Unrealized Gains	35
Gross Unrealized Losses	(71)
Sovereign bonds [Member]
Summary of available-for-sale investments
Fair Value, Short-term investments	4,016	19,350
Fair Value, Long-term investments	22,355	0
Fair Value, Total	26,371
Sovereign bonds [Member] | Short-term investments [Member]
Summary of available-for-sale investments
Amortized Cost	3,973
Gross Unrealized Gains	43
Gross Unrealized Losses	0
Fair Value, Short-term investments	4,016
Sovereign bonds [Member] | Long-term investments [Member]
Summary of available-for-sale investments
Amortized Cost	22,029
Gross Unrealized Gains	326
Gross Unrealized Losses	0
Covered bonds [Member]
Summary of available-for-sale investments
Fair Value, Short-term investments	1,319	0
Fair Value, Long-term investments	4,701	3,541
Fair Value, Total	6,020
Covered bonds [Member] | Short-term investments [Member]
Summary of available-for-sale investments
Amortized Cost	1,317
Gross Unrealized Gains	2
Gross Unrealized Losses	0
Fair Value, Short-term investments	1,319
Covered bonds [Member] | Long-term investments [Member]
Summary of available-for-sale investments
Amortized Cost	4,679
Gross Unrealized Gains	22
Gross Unrealized Losses	$ 0