Acquisitions - Acquisition Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	Mar. 09, 2020	May 09, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Assets
Goodwill			$ 862,397	$ 796,756	$ 728,809	$ 697,608
Park Bank
Assets
Cash and due from banks and interest-bearing deposits in other banks	$ 244,781
Equity securities	0
Securities available-for-sale	136,856
Securities held-to-maturity	300
FHLB and FRB stock	0
Loans	687,923
OREO	2,276
Goodwill	60,632
Other intangible assets	3,068
Premises, furniture, and equipment	2,550
Accrued interest receivable and other assets	12,475
Total assets	1,150,861
Liabilities
Noninterest-bearing deposits	356,050
Interest-bearing deposits	594,026
Total deposits	950,076
Borrowed funds	11,532
Senior and subordinated debt	0
Accrued interest payable and other liabilities	14,871
Total liabilities	$ 976,479
Acquisition, net of issuance costs (in shares)	4,930,231
Consideration Paid
Common stock (2020 - 4,930,231, shares issued at $14.58 per share, 2019 - 4,728,541 share issued at $20.77 per share), net of issuance costs	$ 71,883
Cash paid	102,499
Total consideration paid	$ 174,382
Shares issued (in dollars per share)	$ 14.58
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		709,438
OREO		5,436
Goodwill		63,231
Other intangible assets		15,603
Premises, furniture, and equipment		16,138
Accrued interest receivable and other assets		35,909
Total assets		1,165,815
Liabilities
Noninterest-bearing deposits		179,267
Interest-bearing deposits		807,487
Total deposits	$ 1,000,000	986,754
Borrowed funds		1,746
Senior and subordinated debt		29,360
Accrued interest payable and other liabilities		12,603
Total liabilities		$ 1,030,463
Acquisition, net of issuance costs (in shares)		4,728,541
Consideration Paid
Common stock (2020 - 4,930,231, shares issued at $14.58 per share, 2019 - 4,728,541 share issued at $20.77 per share), net of issuance costs		$ 98,212
Cash paid		37,140
Total consideration paid		$ 135,352
Shares issued (in dollars per share)		$ 20.77