Marketable Securities - Restricted (Unrealized losses on investments restricted from sale) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013 investment	Dec. 31, 2012 investment
Restricted Mutual Funds [Member]
Total Number in Loss Position	1	1
Less than twelve months - fair values	$ 8,127	$ 10,996
Less than twelve months - unrealized losses	(145)	(54)
Twelve months or greater - fair values	0	0
Twelve months or greater - unrealized losses	0	0
Total Fair Value	8,127	10,996
Total Unrealized Losses	(145)	(54)
Total Restricted Available for Sale Securities [Member]
Total Number in Loss Position	1	1
Less than twelve months - fair values	8,127	10,996
Less than twelve months - unrealized losses	(145)	(54)
Twelve months or greater - fair values	0	0
Twelve months or greater - unrealized losses	0	0
Total Fair Value	8,127	10,996
Total Unrealized Losses	$ (145)	$ (54)