Significant Accounting Policies (Notes to Consolidated Financial Statements) (Details) $ in Millions	Sep. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2014 USD ($) Branch	Sep. 30, 2014 USD ($)	Jun. 30, 2014 USD ($)
Accounting Policies [Abstract]
Number of banking offices			367
Unamortized Debt Issuance Expense \| $	$ 3.7	$ 3.8	$ 3.7	$ 1.9	$ 1.8

The remaining balance of debt issuance expenses that were capitalized and are being amortized against income over the lives of the respective bond issues. This does not include the amounts capitalized as part of the cost of the utility plant or asset.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.17)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Name:	us-gaap_UnamortizedDebtIssuanceExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant