Fair Value Measurements - Assets and Liabilities Measured at Fair Value on a Recurring Basis using Significant Unobservable Inputs (Details) (Option contracts [Member], USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2013
Option contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at December 31, 2012	$ 0.3
Total realized or unrealized gains (losses) included in earnings, net	(0.3)
Settlements, net	(0.3)
Balance at June 30, 2013	$ (0.3)