Marketable Securities - Restricted (Unrealized losses on investments restricted from sale) (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013 investment	Dec. 31, 2012 investment
Less than twelve months - fair values	$ 16,843
Less than twelve months - unrealized losses	(490)
Twelve months or greater - fair values	0
Twelve months or greater - unrealized losses	0
Total Fair Value	16,843
Total Unrealized Losses	(490)
Restricted Mutual Funds [Member]
Total Number in Loss Position (investments)	2	1
Less than twelve months - fair values	14,374	10,996
Less than twelve months - unrealized losses	(597)	(54)
Twelve months or greater - fair values	0	0
Twelve months or greater - unrealized losses	0	0
Total Fair Value	14,374	10,996
Total Unrealized Losses	(597)	(54)
Total Restricted Available for Sale Securities [Member]
Total Number in Loss Position (investments)	2	1
Less than twelve months - fair values	14,374	10,996
Less than twelve months - unrealized losses	(597)	(54)
Twelve months or greater - fair values	0	0
Twelve months or greater - unrealized losses	0	0
Total Fair Value	14,374	10,996
Total Unrealized Losses	$ (597)	$ (54)