Fair Value Measurement Fair Value Measurement (Details 1) (USD $) In Thousands, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2012		Sep. 30, 2011		Sep. 30, 2012		Sep. 30, 2011		Mar. 31, 2011
Available-for-sale Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
True-up liability, Beginning balance	$ 48,096				$ 87,539		$ 60,344		$ 144,570
(Gains) losses included in earnings	0		0		0		0
Unrealized gains (losses)	(605)	[1]	(4,549)	[1]	3,137	[1]	(4,199)	[1]
Purchases	0		0		0		83,876
Sales	0		(44,924)		(40,520)		(44,924)
Settlements	13		(4,056)		(2,652)		(4,056)
Net transfers inton (out of) Level 3	0		0		0		0
True-up liability, Ending balance	47,504		91,041		47,504		91,041		144,570
True Up Liability [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
True-up liability, Beginning balance	11,820				11,551		12,061		12,196
(Gains) losses included in earnings	822		(283)		1,091		(148)
Unrealized gains (losses)	0	[1]	0	[1]	0	[1]	0	[1]
Purchases	0		0		0		0
Sales	0		0		0		0
Settlements	0		0		0		0
Net transfers inton (out of) Level 3	0		0		0		0
True-up liability, Ending balance	$ 12,642		$ 11,913		$ 12,642		$ 11,913		$ 12,196

[1] Reported in other