Basis of Presentation (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017 USD ($) shares	Jun. 30, 2016 USD ($) shares	Jun. 30, 2017 USD ($) item shares	Jun. 30, 2016 USD ($) shares
Cash and Cash Equivalents
Number of banks in which the entity has its majority cash balances held in demand deposit accounts | item			1
Supplemental Non-Cash Investing and Financing Activities
Accounts payable | $			$ 19,600	$ 21,500
Taxes Collected from Customers
Excise taxes and Hawaii Public Utility Commission fees | $	$ 2,000	$ 2,000	$ 4,200	$ 4,300
Denominator used to compute basic and diluted earnings per share
Basic earnings per share - weighted average shares	11,587,963	11,511,591	11,558,667	11,493,712
Effect of dilutive securities:
Employee and director restricted stock units (in shares)		14,259		29,503
Diluted earnings per share - weighted average shares	11,587,963	11,525,850	11,558,667	11,523,215
Shares attributable to restricted stock units excluded from computation of weighted average dilutive shares	310,790	152,447	310,790	109,730
Recently Adopted Accounting Pronouncements
Cumulative effect of adoption of new accounting standard for stock compensation | $			$ 550