Other Comprehensive Income (Components of Other Comprehensive Income) (Details) (USD $)	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Other Comprehensive Income
Net income/(loss)	$ 27,016,000	$ 22,304,000	$ 3,416,000	$ 31,398,000	$ 41,394,000	$ (84,336,000)	$ 21,109,000	$ 23,740,000
Unrealized gains on available-for-sale securities, net of tax									2,103,000	3,132,000.0	7,517,000
Unrealized losses in cash flow hedging instruments, net of tax									(9,615,000)	(5,793,000.0)	80,000
Foreign currency translation adjustment, net of tax									(807,000)	1,740,000.0
Other comprehensive income (loss)									(8,319,000)	(921,000.0)	7,597,000
Comprehensive income									$ 75,815,000	$ 986,000.0	$ 83,395,000