Cash, Cash Equivalents and Available for Sale Securities (Details) (USD $)	6 Months Ended	12 Months Ended
	Jun. 30, 2013	Dec. 31, 2012
Restricted Cash and Cash Equivalents Items [Line Items]
Cash	$ 255,100,000	$ 504,700,000
Investments in cash equivalents	37,800,000	14,700,000
Cost	8,107,000	50,865,000
Available for sale securities (Fair value/Carrying value)	8,112,000	50,875,000
Unrealized Gain	5,000	10,000
Restricted cash	1,558,000	1,571,000
Restricted cash outstanding, letters of credit used for collateral	1,000,000	1,000,000
Restricted cash guaranteed, investment certificate for collateral	300,000	300,000
Restricted cash and cash equivalents, foreign tender	300,000	300,000
U.S. government agencies notes [Member]
Restricted Cash and Cash Equivalents Items [Line Items]
Cost	0	7,093,000
Available for sale securities (Fair value/Carrying value)	0	7,097,000
Unrealized Gain	0	4,000
Corporate debt securities [Member]
Restricted Cash and Cash Equivalents Items [Line Items]
Cost	8,107,000	43,772,000
Available for sale securities (Fair value/Carrying value)	8,112,000	43,778,000
Unrealized Gain	$ 5,000	$ 6,000