Commitments and contingencies - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended	12 Months Ended
Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Commitments and Contingencies Disclosure [Abstract]
Floating interest rate loan commitments			$ 1,820,000		$ 1,650,000
Total principal amount of loans repurchased or indemnified	$ 761	$ 1,568	$ 1,469	$ 4,367

Reflects the amount of cash required to fully fund agreements to provide advances to borrowers and lessees at interest rates that increase or decrease depending on certain facts or circumstances.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 825
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=123345438&loc=d3e61082-112788

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 825
-Section 50
-Paragraph 1
-Subparagraph (b)(2)
-URI http://asc.fasb.org/extlink&oid=123345438&loc=d3e61044-112788

Name:	us-gaap_LoansAndLeasesReceivableCommitmentsVariableRates
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration