Fair Value Measurement Fair Value Measurement (Details 1) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012		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	$ 87,539		$ 60,344
(Gains) losses included in earnings	0		0
Unrealized gains (losses)	2,419	[1]	2,694	[1]
Purchases	0		63,876
Sales	0		0
Settlements	(1,471)		0
Net transfers inton (out of) Level 3	0		0
True-up liability, Ending balance	88,487		126,914
True Up Liability [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
True-up liability, Beginning balance	11,551		12,061
(Gains) losses included in earnings	174		(460)
Unrealized gains (losses)	0	[1]	0	[1]
Purchases	0		0
Sales	0		0
Settlements	0		0
Net transfers inton (out of) Level 3	0		0
True-up liability, Ending balance	$ 11,725		$ 11,601

[1] Reported in other comprehensive income (loss)