Marketable Securities (Realized and Unrealized Gain and Losses) (Details) (USD $)	1 Months Ended	12 Months Ended
	Jan. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Sales Transaction of Marketable Securities, Unrealized Gain (Loss) [Abstract]
Equity securities, carrying value		$ 22,168,000	$ 20,884,000	$ 51,300,000
Marketable securities, realized gain		0	24,900,000	300,000
Equity securities, gross unrealized gain, before tax				24,200,000
Equity securities, gross unrealized gain, after tax				14,100,000
Equity securities, sale proceeds	51,900,000
Equity securities, gross realized gain, pre-tax	$ 24,900,000