Investment in TRIP Holdings (Details) (USD $) In Millions	Jun. 30, 2011	Dec. 31, 2010
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures [Abstract]
Capital contributions	$ 47.3	$ 47.3
Equity purchased from investors	44.8	44.8
Total investment	92.1	92.1
Equity in earnings	11.5	7.5
Equity in unrealized gains (losses) on derivative financial instruments	(0.8)	(1.4)
Distributions	(7.0)	(7.0)
Deferred broker fees	(0.7)	(0.8)
Carrying Value of TRIP Holdings	$ 95.1	$ 90.4