CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Statement of Comprehensive Income [Abstract]
Net income	$ 167.2	$ 169.2	$ 111.6
Other comprehensive income (loss):
Change in fair value of cash flow swaps	2.3	(3.1)	(2.9)
Income tax (expense) benefit associated with cash flow swaps	(0.9)	1.1	1.2
Comprehensive income (loss)	$ 168.6	$ 167.2	$ 109.9