Allowance for credit losses - Troubled debt restructuring according to their accruing status - Subnote (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Financing Receivable
Aggregated unpaid principal balance		$ 1,223,205
Mortgages
Financing Receivable
Aggregated unpaid principal balance		624,368
Mortgages \| Guaranteed by us sponsored entities
Financing Receivable
Aggregated unpaid principal balance	$ 655,000	$ 625,000

Amount of unpaid principal balance of impaired financing receivables with related allowance for credit losses and without related allowance for credit losses.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (a)(4)
-URI http://asc.fasb.org/extlink&oid=118936363&loc=d3e5212-111524

Name:	us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant