Accounting Policies (Details) $ in Millions	9 Months Ended
	Sep. 30, 2015 USD ($) segment States	Dec. 31, 2014 USD ($)
Revenues from External Customers and Long-Lived Assets [Line Items]
Current customer deposits	$ 2.2	$ 2.4
Estimated fair value exceeded the carrying value, percent		4.00%
Number of operating segments | segment	1
Number of operating states | States	17
Other Accrued Liabilities
Revenues from External Customers and Long-Lived Assets [Line Items]
Deferred revenue	$ 21.5	$ 19.0
Other Long Term Liabilities
Revenues from External Customers and Long-Lived Assets [Line Items]
Non-current deferred revenue	$ 7.6	$ 9.3