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Organization and Summary of Significant Accounting Policies - Transition to an Independent Public Company (Details) - First Hawaiian, Inc. (FHI) - USD ($)		12 Months Ended
	Feb. 01, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
BNP Paribas (BNPP)
Reorganization Transactions
Outstanding common stock owned after sales of shares (as a percent)	0.00%
Completion of public offering
Reorganization Transactions
Proceeds from the sales of shares		$ 0	$ 0	$ 0