Commitments and Contingent Liabilities - Contingencies (Details)	3 Months Ended
Mar. 31, 2018 USD ($)
Overdraft fee litigation
Contingencies
Loss contingency liability	$ 0
First Hawaiian Bank
Contingencies
Period for one-time continuous negative balance overdraft fee	7 days

Amount of loss contingency liability.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=82911808&loc=d3e14326-108349

Name:	us-gaap_LossContingencyAccrualAtCarryingValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant