Investment Securities (Details 6) (Terre Star Network Inc., 6 1/2 % Senior Exchangeable Paid-In-Kind Notes Due June 15, 2014, USD $) In Millions, unless otherwise specified	1 Months Ended	9 Months Ended
	Feb. 29, 2008	Sep. 30, 2013	Dec. 31, 2012
Terre Star Network Inc. | 6 1/2 % Senior Exchangeable Paid-In-Kind Notes Due June 15, 2014
Marketable investment securities:
Aggregate principal amount of investment acquired	$ 50.0
Interest rate (as a percent)		6.50%
Aggregate principal amount of investment held		$ 0	$ 0