Regulatory Capital Requirements (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Common equity tier 1 capital to risk-weighted assets
Actual Amount	$ 1,690,054	$ 1,633,442
Actual Ratio (as a percent)	12.73%	12.45%
Minimum Capital Ratio (as a percent)	4.50%	4.50%
Well-Capitalized Ratio (as a percent)	6.50%	6.50%
Tier 1 capital to risk-weighted assets
Actual Amount	$ 1,690,054	$ 1,633,442
Actual Ratio (as a percent)	12.73%	12.45%
Minimum Capital Ratio (as a percent)	6.00%	6.00%
Well-Capitalized Ratio (percent)	8.00%	8.00%
Total capital to risk-weighted assets
Actual Amount	$ 1,829,228	$ 1,771,295
Actual Ratio (as a percent)	13.77%	13.50%
Minimum Capital Ratio (as a percent)	8.00%	8.00%
Well-Capitalized Ratio (as a percent)	10.00%	10.00%
Tier 1 capital to average assets (leverage ratio)
Actual Amount	$ 1,690,054	$ 1,633,442
Actual Ratio	8.71%	8.52%
Minimum Capital Ratio (as a percent)	4.00%	4.00%
Well-Capitalized Ratio (percent)	5.00%	5.00%
First Hawaiian Bank
Common equity tier 1 capital to risk-weighted assets
Actual Amount	$ 1,688,288	$ 1,623,455
Actual Ratio (as a percent)	12.71%	12.37%
Tier 1 capital to risk-weighted assets
Actual Amount	$ 1,688,288	$ 1,623,455
Actual Ratio (as a percent)	12.71%	12.37%
Total capital to risk-weighted assets
Actual Amount	$ 1,827,462	$ 1,761,308
Actual Ratio (as a percent)	13.76%	13.42%
Tier 1 capital to average assets (leverage ratio)
Actual Amount	$ 1,688,288	$ 1,623,455
Actual Ratio	8.70%	8.47%