CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 184.4	$ 168.0	$ 139.1
Other comprehensive income (loss):
Change in fair value of cash flow swaps	(4.4)	2.3	1.9
Income tax benefit (expense) associated with cash flow swaps	1.1	(0.8)	(0.7)
Comprehensive income	$ 181.1	$ 169.5	$ 140.3