Regulatory Capital Requirements (Details) $ in Thousands	Sep. 30, 2023 USD ($)	Dec. 31, 2022 USD ($)
Common equity tier 1 capital to risk-weighted assets
Amount	$ 2,004,248	$ 1,912,767
Ratio (as a percent)	0.1221	0.1182
Minimum Capital Ratio (as a percent)	0.0450	0.0450
Well-Capitalized Ratio (as a percent)	0.0650	0.0650
Tier 1 capital to risk-weighted assets
Amount	$ 2,004,248	$ 1,912,767
Ratio (as a percent)	0.1221	0.1182
Minimum Capital Ratio (as a percent)	0.0600	0.0600
Well-Capitalized Ratio (percent)	0.0800	0.0800
Total capital to risk-weighted assets
Amount	$ 2,196,818	$ 2,090,502
Ratio (as a percent)	0.1338	0.1292
Minimum Capital Ratio (as a percent)	0.0800	0.0800
Well-Capitalized Ratio (as a percent)	0.1000	0.1000
Tier 1 capital to average assets (leverage ratio)
Amount	$ 2,004,248	$ 1,912,767
Ratio	0.0845	0.0811
Minimum Capital Ratio (as a percent)	0.0400	0.0400
Well-Capitalized Ratio (percent)	0.0500	0.0500
First Hawaiian Bank (FHB)
Common equity tier 1 capital to risk-weighted assets
Amount	$ 1,990,261	$ 1,895,693
Ratio (as a percent)	0.1212	0.1171
Tier 1 capital to risk-weighted assets
Amount	$ 1,990,261	$ 1,895,693
Ratio (as a percent)	0.1212	0.1171
Total capital to risk-weighted assets
Amount	$ 2,182,831	$ 2,073,428
Ratio (as a percent)	0.1330	0.1281
Tier 1 capital to average assets (leverage ratio)
Amount	$ 1,990,261	$ 1,895,693
Ratio	0.0839	0.0804