Goodwill and Core Deposit Intangibles (Tables)

12 Months Ended

Dec. 31, 2018

Goodwill and Intangible Assets Disclosure [Abstract]

Change in Carrying Amount of Goodwill

Goodwill
	Year Ended December 31,
	2018		2017
Net carrying value at beginning of period	$	444.7	$	212.8
Acquisitions and measurement period adjustments	102.0		231.9
Net carrying value at end of period	$	546.7	$	444.7

Schedule of Activity of Identifiable Core Deposit Intangibles

Core deposit intangibles (“CDI”) The following table sets forth activity for identifiable core deposit intangibles subject to amortization:
	Year Ended December 31,
	2018			2017
Gross CDI, beginning of period	$	74.0		$	29.2
Established through acquisitions	15.7			48.0
Reductions due to sale of accounts	—			(3.2		)
Accumulated amortization	(32.8		)	(24.9		)
Net CDI, end of period	$	56.9		$	49.1

Schedule of Finite-Lived Intangible Assets, Future Amortization Expense

The following table provides estimated future CDI amortization expense:

Years ending December 31,
2019	$	8.9
2020	8.1
2021	7.5
2022	6.9
2023	6.3
Thereafter	19.2
Total	$	56.9