Goodwill and Core Deposit Intangibles (Tables)

12 Months Ended

Dec. 31, 2019

Goodwill and Intangible Assets Disclosure [Abstract]

Change in Carrying Amount of Goodwill

Goodwill
	Year Ended December 31,
	2019		2018
Net carrying value at beginning of period	$	546.7	$	444.7
Acquisitions and measurement period adjustments	74.9		102.0
Net carrying value at end of period	$	621.6	$	546.7

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,
	2019			2018
Gross CDI, beginning of period	$	89.7		$	74.0
Established through acquisitions	16.6			15.7
Reductions due to sale of accounts	(0.3		)	—
Accumulated amortization	(43.9		)	(32.8		)
Net CDI, end of period	$	62.1		$	56.9

Schedule of Finite-Lived Intangible Assets, Future Amortization Expense

The following table provides estimated future CDI amortization expense:

Years ending December 31,
2020	$	10.9
2021	9.9
2022	9.0
2023	8.2
2024	7.3
Thereafter	16.8
Total	$	62.1