Segment reporting - Additional Information (Details) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) segment	Sep. 30, 2019 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments \| segment			2
Other noninterest expense	$ 69,898	$ 36,710	$ 150,352	$ 109,447
Relief of goodwill due to sale of TPO mortgage delivery channel			0	100
Interest income	76,504	67,639	201,350	194,363
Mortgage Segment
Segment Reporting Information [Line Items]
Other noninterest expense	330	112	330	1,995
Relief of goodwill due to sale of TPO mortgage delivery channel		100		100
Interest paid	$ 3,940	$ 2,875	$ 9,650	$ 8,723
Mortgage Segment \| Prime Interest Rate
Segment Reporting Information [Line Items]
Warehouse line of credit interest rate	3.25%	5.00%	3.25%	5.00%
Banking Segment
Segment Reporting Information [Line Items]
Other noninterest expense	$ 69,568	$ 36,598	$ 150,022	$ 107,452
Interest income	$ 3,940	$ 2,875	$ 9,650	$ 8,723

Goodwill, Relief (Written off) Related to Sale of Business Unit

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- Definition

Interest and Fee Income, Loans

+ References

No definition available.

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Amount of cash paid for interest, including, but not limited to, capitalized interest and payment to settle zero-coupon bond attributable to accreted interest of debt discount and debt instrument with insignificant coupon interest rate in relation to effective interest rate of borrowing attributable to accreted interest of debt discount; classified as operating and investing activities.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=121583591&loc=d3e4297-108586

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- Definition

The effective interest rate at the end of the reporting period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.19(b),22(b))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

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- Definition

Number of segments reported by the entity. A reportable segment is a component of an entity for which there is an accounting requirement to report separate financial information on that component in the entity's financial statements.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 18
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8672-108599

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- Definition

Amount of noninterest expense classified as other.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04.14)
-URI http://asc.fasb.org/extlink&oid=120399700&loc=SL114874048-224260

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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