Operating Lease Right-of-Use Assets and Liabilities - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Lessee, Lease, Description [Line Items]
Operating lease right-of-use assets	$ 106,700	$ 118,700
Lease liabilities	122,848	138,400
Leases not yet commenced, amount	$ 231,600
Ownership percentage	50.00%
Corporate Headquarters
Lessee, Lease, Description [Line Items]
Leases not yet commenced, term	22 years 6 months
Chemical Financial Corporation
Lessee, Lease, Description [Line Items]
Operating lease right-of-use assets		39,800
Lease liabilities		$ 41,600