Basis of Presentation (Details) $ in Millions	3 Months Ended
	Mar. 31, 2016 USD ($) item shares	Mar. 31, 2015 USD ($) 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 | $	$ 17.0	$ 15.2
Taxes Collected from Customers
Excise taxes and Hawaii Public Utility Commission fees | $	$ 2.2	$ 2.0
Denominator used to compute basic and diluted earnings per share
Basic earnings per share - weighted average shares	11,475,834	10,692,198
Effect of dilutive securities:
Employee and director restricted stock units (in shares)	24,474	73,457
Warrants (in shares)		507,267
Diluted earnings per share - weighted average shares	11,500,308	11,272,922
Shares attributable to restricted stock units excluded from computation of weighted average dilutive shares	135,906	0