CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Cash Flows from Operating Activities
Net income	$ 40,864	$ 33,883	$ 29,586
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	69,287	63,324	56,583
Amortization	1,415	2,566	4,139
Provision for bad debt	1,640	1,678	2,019
Stock based compensation expense	2,333	2,624	1,938
Excess tax benefits on stock option exercises	(679)	(395)	(101)
Deferred income taxes	(451)	2,975	14,266
Net loss on disposal of equipment	235	1,975	753
Realized loss on disposal of investments	20	0	1
Unrealized (gains) loss on investments	141	51	(391)
Net gains from patronage and equity investments	(805)	(852)	(837)
Amortization of long term debt issuance costs	567	605	609
Other	93	1,515	1,663
(Increase) decrease in:
Accounts receivable	(1,047)	(6,225)	(2,594)
Materials and supplies	492	1,921	(927)
Income taxes receivable	7,058	1,824	(11,871)
Other assets	(6,368)	1,055	(1,034)
Increase (decrease) in:
Accounts payable	2,753	5,040	(2,145)
Deferred lease payable	962	1,024	1,253
Other deferrals and accruals	811	405	1,354
Net cash provided by operating activities	119,321	114,993	94,264
Cash Flows from Investing Activities
Acquisition of property, plant and equipment	(69,679)	(68,232)	(117,028)
Proceeds from sale of equipment	363	551	331
Proceeds from sales of assets	0	0	25
Purchase of investment securities	0	0	(12)
Cash distributions from investments	54	43	121
Net cash used in investing activities	(69,262)	(67,638)	(116,563)
Cash Flows From Financing Activities
Principal payments on long-term debt	(23,000)	(5,750)	(1,977)
Cash paid for debt issuance costs	(7,880)	0	0
Dividends paid, net of dividends reinvested	(11,085)	(10,761)	(8,191)
Excess tax benefits on stock option exercises	679	395	101
Repurchases of common stock	(1,885)	(1,785)	(1,600)
Proceeds from issuances of common stock	1,007	1,147	1,196
Net cash used in financing activities	(42,164)	(16,754)	(10,471)
Net increase (decrease) in cash and cash equivalents	7,895	30,601	(32,770)
Cash and cash equivalents:
Beginning	68,917	38,316	71,086
Ending	76,812	68,917	38,316
Cash payments for:
Interest, net of capitalized interest of $436 in 2015, $373 in 2014, and $396 in 2013	6,784	7,548	8,077
Income taxes paid, net	$ 21,119	$ 17,233	$ 17,483