Significant group concentrations of credit risk (Details)	12 Months Ended
Dec. 31, 2020
Major customers
Percentage of benchmark loan to appraisal ratio in excess of which mortgage insurance is required	80.00%
Percentage of workforce covered by collective bargaining arrangement	50.00%
American Savings Bank (ASB)
Major customers
Percentage of benchmark loan to appraisal ratio in excess of which mortgage insurance is required	80.00%

Percentage of entity's employees covered by collective-bargaining arrangement (CBA) to all participants in multiemployer pension plan determined to be individually insignificant.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 80
-Section 50
-Paragraph 5
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=65877416&loc=SL14450657-114947

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration