Acquisitions - Acquisition Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	May 09, 2019	Oct. 12, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Assets
Goodwill			$ 796,756	$ 728,809	$ 697,608	$ 340,879
Northern States Financial Corporation
Assets
Cash and due from banks and interest-bearing deposits in other banks		$ 160,145
Equity securities		3,915
Securities available-for-sale		47,149
Securities held-to-maturity		0
FHLB and FRB stock		554
Loans		284,940
OREO		2,549
Investment in BOLI		11,104
Goodwill		30,016
Other intangible assets		12,230
Premises, furniture, and equipment		5,820
Accrued interest receivable and other assets		20,911
Total assets		579,333
Liabilities
Noninterest-bearing deposits		346,714
Interest-bearing deposits		116,446
Total deposits		463,160
Borrowed funds		18,218
Senior and subordinated debt		8,038
Accrued interest payable and other liabilities		6,614
Total liabilities		496,030
Consideration Paid
Common stock (2019 - 4,728,541, shares issued at $28.61 per share, 2018 - 3,310,912 share issued at $25.16 per share), net of issuance costs		83,303
Cash paid		0
Total consideration paid		$ 83,303
Common stock, shares issued (in shares)		3,310,912
Shares issued (in dollars per share)		$ 25.16
Bridgeview Bancorp, Inc.
Assets
Cash and due from banks and interest-bearing deposits in other banks	$ 35,097
Equity securities	6,966
Securities available-for-sale	263,090
Securities held-to-maturity	13,426
FHLB and FRB stock	1,481
Loans	710,647
OREO	6,003
Investment in BOLI	0
Goodwill	59,142
Other intangible assets	15,603
Premises, furniture, and equipment	17,681
Accrued interest receivable and other assets	35,997
Total assets	1,165,133
Liabilities
Noninterest-bearing deposits	179,267
Interest-bearing deposits	807,487
Total deposits	986,754
Borrowed funds	1,746
Senior and subordinated debt	29,360
Accrued interest payable and other liabilities	11,921
Total liabilities	1,029,781
Consideration Paid
Common stock (2019 - 4,728,541, shares issued at $28.61 per share, 2018 - 3,310,912 share issued at $25.16 per share), net of issuance costs	98,212
Cash paid	37,140
Total consideration paid	$ 135,352
Common stock, shares issued (in shares)	4,728,541
Shares issued (in dollars per share)	$ 28.61