Investment Securities (Municipal Bonds Narrative) (Details 6) - HAWAII $ in Millions	3 Months Ended
	Mar. 31, 2019 USD ($)
Debt Securities Issued by States and Political Subdivisions
Debt Securities, Available-for-sale [Line Items]
Debt Securities Issued by State and Political Subdivision, State of Hawaii	$ 408.8
Municipal Debt Securities | Geographic Concentration Risk | Debt Securities Issued by States and Political Subdivisions
Debt Securities, Available-for-sale [Line Items]
Concentration risk, percentage	98.00%
Hawaiian Municipal Debt Securities | Investment Concentration Risk | General Obligation Bond
Debt Securities, Available-for-sale [Line Items]
Concentration risk, percentage	80.00%
Moody's, Aa2 Rating (or better) | Hawaiian Municipal Debt Securities | Investment Concentration Risk | Debt Securities Issued by States and Political Subdivisions
Debt Securities, Available-for-sale [Line Items]
Concentration risk, percentage	94.00%