Acquisition and Divestiture Activity - Schedule of Acquired Loan Data (Detail) - Minnesota [Member] - USD ($) $ in Thousands	Nov. 01, 2018	Jun. 30, 2018
Anchor Bank (MN) [Member]
Loans at Acquisition Date [Line Items]
Fair Value of Acquired Loans at Acquisition Date		$ 1,593,991
Anchor Bank (MN) [Member] \| Acquired Receivables Subject to ASC 310-30 [Member]
Loans at Acquisition Date [Line Items]
Fair Value of Acquired Loans at Acquisition Date		10,555
Gross Contractual Cash Flows at Acquisition Date		16,898
Best Estimate at Acquisition Date of Contractual Cash Flows Not Expected to be Collected		4,787
Anchor Bank (MN) [Member] \| Acquired Receivables Not Subject to ASC 310-30 [Member]
Loans at Acquisition Date [Line Items]
Fair Value of Acquired Loans at Acquisition Date		1,583,436
Gross Contractual Cash Flows at Acquisition Date		1,879,449
Best Estimate at Acquisition Date of Contractual Cash Flows Not Expected to be Collected		$ 87,767
KleinBank [Member]
Loans at Acquisition Date [Line Items]
Fair Value of Acquired Loans at Acquisition Date	$ 1,049,073
KleinBank [Member] \| Acquired Receivables Subject to ASC 310-30 [Member]
Loans at Acquisition Date [Line Items]
Fair Value of Acquired Loans at Acquisition Date	11,663
Gross Contractual Cash Flows at Acquisition Date	18,568
Best Estimate at Acquisition Date of Contractual Cash Flows Not Expected to be Collected	4,521
KleinBank [Member] \| Acquired Receivables Not Subject to ASC 310-30 [Member]
Loans at Acquisition Date [Line Items]
Fair Value of Acquired Loans at Acquisition Date	1,037,410
Gross Contractual Cash Flows at Acquisition Date	1,252,954
Best Estimate at Acquisition Date of Contractual Cash Flows Not Expected to be Collected	$ 76,534

Loans at Acquisition Date [Line Items]

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- Definition

For receivables acquired in a business combination, excluding certain loans and debt securities acquired in a transfer (as defined), this element represents the best estimate at the acquisition date of the contractual cash flows not expected to be collected, by major class of receivable, such as loans, direct finance leases (as defined), and any other class of receivables.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (b)(3)
-URI http://asc.fasb.org/extlink&oid=84161108&loc=d3e4845-128472

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- Definition

Fair value of acquired receivable from business combination, excluding certain loans and debt securities acquired in transfer.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=84161108&loc=d3e4845-128472

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- Definition

For receivables acquired in a business combination, excluding certain loans and debt securities acquired in a transfer (as defined), this element represents the gross contractual amounts receivable, by major class of receivable, such as loans, direct finance leases (as defined), and any other class of receivables.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (b)(2)
-URI http://asc.fasb.org/extlink&oid=84161108&loc=d3e4845-128472

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