Regulatory Capital and Dividends - Narrative (Details) - USD ($)		4 Months Ended	12 Months Ended
	Sep. 01, 2019	Dec. 31, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Sep. 03, 2019
Restructuring Cost and Reserve [Line Items]
Dividends available			$ 189,371,000
Dividend reinvestment and stock purchase plan, stockholder's maximum amount of cash payments per quarter in purchase of common stock			5,000
Issuance of common stock related to acquisitions			229,926,000	$ 0	$ 321,431,000
Repurchases of common stock			$ 19,041,000
Stock Repurchase Program
Restructuring Cost and Reserve [Line Items]
Stock authorized to be repurchased (in shares)						3,000,000
Stock authorized to be repurchased						$ 75,000,000
Percent of outstanding shares						5.00%
Repurchases of common stock (in shares)		516,016
Repurchases of common stock		$ 19,000,000.0
Average price (in usd per share)		$ 36.90
MBT
Restructuring Cost and Reserve [Line Items]
Percentage of interest acquired	100.00%
Common Stock
Restructuring Cost and Reserve [Line Items]
Number of shares of common stock	0.275
Stock issued as a part of acquisition (in shares)			6,383,806		8,044,446
Issuance of common stock related to acquisitions			$ 798,000		$ 1,006,000
Repurchases of common stock (in shares)			516,016
Repurchases of common stock			$ 65,000
Common Stock | MBT
Restructuring Cost and Reserve [Line Items]
Number of shares of common stock	0.275
Stock issued as a part of acquisition (in shares)	6,400,000
Issuance of common stock related to acquisitions	$ 229,900,000