CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Statement of Comprehensive Income [Abstract]
Net income	$ 51.1	$ 32.5	$ 128.1	$ 99.8
Other comprehensive income:
Change in fair value of cash flow swaps	(4.0)	0.1	(5.0)	(1.7)
Income tax benefit associated with cash flow swaps	1.5	0.0	1.9	0.7
Comprehensive income	$ 48.6	$ 32.6	$ 125.0	$ 98.8