Acquisition - Acquisitions Narrative (Details)		12 Months Ended
	Sep. 01, 2019 USD ($) bank_branch shares	Dec. 31, 2019 USD ($) shares	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($) shares
Business Acquisition [Line Items]
Issuance of common stock related to acquisitions		$ 229,926,000	$ 0	$ 321,431,000
Common Stock
Business Acquisition [Line Items]
Number of shares of common stock	0.275
Stock issued as a part of acquisition (in shares) | shares		6,383,806		8,044,446
Issuance of common stock related to acquisitions		$ 798,000		$ 1,006,000
MBT
Business Acquisition [Line Items]
Percentage of interest acquired	100.00%
Number of banking centers acquired | bank_branch	20
Other intangible assets	$ 16,527,000
Operating revenue		19,700,000
Non-recurring expenses		$ 19,700,000	$ 877,000
MBT | Core deposit intangible acquired
Business Acquisition [Line Items]
Other intangible assets	$ 16,527,000
Acquired intangible asset, expected useful life	10 years
MBT | Common Stock
Business Acquisition [Line Items]
Number of shares of common stock	0.275
Stock issued as a part of acquisition (in shares) | shares	6,400,000
Issuance of common stock related to acquisitions	$ 229,900,000