Regulatory Capital Requirements (Details) $ in Thousands	Sep. 30, 2024 USD ($)	Dec. 31, 2023 USD ($)
Common equity tier 1 capital to risk-weighted assets
Amount	$ 2,105,200	$ 2,020,784
Ratio (as a percent)	0.1303	0.1239
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	$ 2,105,200	$ 2,020,784
Ratio (as a percent)	0.1303	0.1239
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	$ 2,302,597	$ 2,212,922
Ratio (as a percent)	0.1425	0.1357
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	$ 2,105,200	$ 2,020,784
Ratio	0.0914	0.0864
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	$ 2,091,548	$ 2,006,393
Ratio (as a percent)	0.1294	0.1230
Tier 1 capital to risk-weighted assets
Amount	$ 2,091,548	$ 2,006,393
Ratio (as a percent)	0.1294	0.1230
Total capital to risk-weighted assets
Amount	$ 2,288,945	$ 2,198,531
Ratio (as a percent)	0.1416	0.1348
Tier 1 capital to average assets (leverage ratio)
Amount	$ 2,091,548	$ 2,006,393
Ratio	0.0908	0.0857