Allowance for Credit Losses - Aging of Past-Due Receivables (Details) (Notes Receivable [Member], USD $) In Millions, unless otherwise specified	Mar. 31, 2015		Dec. 31, 2014
Notes Receivable [Member]
Summarizes the Company's aging of past-due notes receivable
30-59 days past due	$ 0		$ 0.1
60-89 days past due	0		0
89 days past due (1)	2.3	[1]	1.5	[1]
Total past due	$ 2.3		$ 1.6

[1] Past-due notes receivable balances greater than 89 days are fully reserved.