Operating Lease Right-of-Use Assets and Liabilities - Narrative (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Aug. 01, 2019
Lessee, Lease, Description [Line Items]
Operating lease right-of-use assets	$ 114,200
Lease liabilities	135,143
Leases not yet commenced, amount	250,100
Chemical Financial Corporation
Lessee, Lease, Description [Line Items]
Operating lease right-of-use assets	39,800	$ 39,800
Lease liabilities	41,600	$ 41,600
Corporate Headquarters
Lessee, Lease, Description [Line Items]
Leases not yet commenced, amount	$ 231,700
Leases not yet commenced, term	22 years 6 months