Significant Accounting Policies - Allowance for Doubtful Accounts (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at Beginning of year	$ 1.3	$ 1.6	$ 1.7
Provision for bad debt	0.8	0.1	0.2
Write-offs and Other	(0.4)	(0.4)	(0.3)
Balance at End of Year	$ 1.7	$ 1.3	$ 1.6