Goodwill and Intangibles - Schedule of Finite-Lived Intangible Assets (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Gross CDI, beginning of period	$ 89.7	$ 74.0
Accumulated amortization	(35.1)	(26.7)
Net CDI, end of period	54.6	47.3
Goodwill [Roll Forward]
Net carrying value at beginning of three month period	546.7	444.7
Net increase to goodwill	(0.4)	0.9
Net carrying value at end of period	$ 546.3	$ 445.6