Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Operating activities:
Net income	$ 47,254	$ 48,828	$ 37,712
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	60,250	56,866	51,981
Amortization of debt premium and expenses	1,081	1,107	1,082
Changes in deferred income taxes	9,800	34,133	2,723
Other changes in noncurrent assets and liabilities	10,244	(9,932)	(689)
Change in value of life insurance contracts	(1,878)	(2,504)	1,876
Stock-based compensation	1,832	1,442	1,300
(Gain) on sale of non-utility property		(84)	(62)
Changes in operating assets and liabilities:
Receivables	(7,201)	(1,392)	(8,213)
Unbilled revenue	(1,640)	(326)	(1,143)
Taxes, prepaid expenses, and other assets	1,490	(3,322)	11,823
Accounts payable	3,809	879	4,612
Other current liabilities	(868)	6,219	8,270
Net cash provided by operating activities	124,173	131,914	111,272
Investing activities:
Utility plant expenditures	(122,988)	(127,681)	(118,546)
Proceeds from sale of non-utility assets		85	64
Purchase of life insurance	(3,281)	(3,294)	(1,744)
Change in restricted cash	1,073	1,959	(3,042)
Net cash used in investing activities	(125,196)	(128,931)	(123,268)
Financing activities:
Short-term borrowings	70,615	94,335	23,390
Repayment of short-term borrowings	(113,275)	(52,000)
Issuance of common stock	110,688		965
Common stock issuance cost	(5,111)
Issuance of long-term debt	48	124	178
Advances and contributions in aid of construction	10,563	6,966	7,231
Refunds of advances for construction	(6,922)	(7,397)	(6,205)
Retirement of long-term debt	(47,248)	(7,037)	(2,963)
Dividends paid	(29,619)	(26,387)	(25,674)
Net cash (used in) provided by financing activities	(10,261)	8,604	(3,078)
Change in cash and cash equivalents	(11,284)	11,587	(15,074)
Cash and cash equivalents at beginning of year	38,790	27,203	42,277
Cash and cash equivalents at end of year	27,506	38,790	27,203
Supplemental disclosures of cash flow information:
Interest (net of amounts capitalized)	28,171	27,120	26,998
Income taxes	7,700		10,535
Income tax refunds		(5,349)	(11,028)
Supplemental disclosure of non-cash activities:
Accrued payables for investments in utility plant	9,932	11,048	9,008
Utility plant contributed by developers	17,329	13,630	14,991
Litigation proceeds for MTBE contamination reclassified from other long-term liabilities to CIAC	7,029	4,462	16,735
Capital leases			$ 9,388