Fair Value Measurement (Details 2) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Available-for-sale securities, Beginning balance	$ 60,344	$ 42,447
True-up liability, Beginning balance	12,061	0
Available-for-sale securities, Total unrealized gains/losses	0	0
True-up liability, Total unrealized gains/losses	(510)	614
Available-for-sale securities, Total changes in fair values included in current period earnings	(1,065)	17,897
True-up liability, Total changes in fair values included in current period earnings	0	0
Available-for-sale securities, Purchases	83,876	0
True-up liability, Purchases	0	11,447
Available-for-sale securities, Sales	(44,924)	0
True-up liability, Sales	0	0
Available-for-sale securities, Settlements	(10,692)	0
True-up liability, Settlements	0	0
Available-for-sale securities, Transfers	0	0
True-up liability, Transfers	0	0
Available-for-sale securities, Ending balance	87,539	60,344
True-up liability, Ending balance	$ 11,551	$ 12,061