Acquisition - Assets Acquired and Liabilities Assumed (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Sep. 01, 2019	Dec. 31, 2018	Dec. 31, 2017
Business Acquisition [Line Items]
Goodwill	$ 543,918		$ 445,355	$ 445,355
MBT
Business Acquisition [Line Items]
Cash and cash equivalents		$ 10,222
Interest-bearing time deposits		281,228
Investment securities		212,235
Loans		732,578
Premises and equipment		21,664
Federal Home Loan Bank stock		4,148
Cash surrender value of life insurance		3,361
Tax asset, deferred and receivable		59,545
Business Combination Recognized Identifiable Assets Acquired and Liabilities Assumed, Deferred Tax Assets		5,205
Other assets		6,011
Deposits		(1,105,926)
Securities sold under repurchase agreements		(94,760)
Federal Home Loan Bank advances		(10,853)
Other liabilities		(9,807)
Net tangible assets acquired		114,851
Core deposit intangible		16,527
Goodwill		98,563
Purchase price		$ 229,941