Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Cash flows from continuing operating activities
Net income	$ 58,604	$ 83,842	$ 29,574
Adjustments to reconcile net income to net cash provided by continuing operating activities:
Net loss from discontinued operations	182	142	141
Deferred income taxes	245	8,688	2,310
Losses on extinguishment of debt		136	52
Expense associated with modification of secured term loan		387
Expense associated with induced conversion of 5.5% convertible debentures		558
Net gains on carbon credits	(155)	(151)
Losses on sales and disposals of property and equipment	996	1,280	460
Gains on property insurance recoveries associated with property, plant and equipment			(7,500)
Depreciation, depletion and amortization of property, plant and equipment	20,681	18,762	17,329
Amortization of other assets	328	440	651
Stock-based compensation	1,652	1,099	1,005
Provisions for (recovery of) losses on accounts receivable	(214)	347	145
Provisions for losses on inventory	1,140	590	184
Provision for (realization of) losses on firm sales commitments	212		(371)
Equity in earnings of affiliate	(681)	(543)	(1,003)
Distributions received from affiliate	1,782	1,649	825
Changes in fair value of commodities contracts	(79)	(11)	(761)
Changes in fair value of interest rate contracts	(367)	346	(34)
Other			(10)
Cash provided (used) by changes in assets and liabilities (net of effects of discontinued operations):
Accounts receivable	7,935	(13,451)	(17,340)
Inventories	(6,607)	60	(9,277)
Prepaid and accrued income taxes	11,013	(12,805)	5,947
Other supplies, prepaid items and other	(2,254)	(8,755)	(1,585)
Accounts payable	980	2,175	15,556
Commodities contracts	11	761	150
Customer deposits	3,684	1,919	1,951
Other current and noncurrent liabilities	383	2,506	5,802
Net cash provided by continuing operating activities	99,471	89,971	44,201
Cash flows from continuing investing activities
Capital expenditures	(92,644)	(44,221)	(34,475)
Acquisition of working interests in natural gas properties	(50,219)
Proceeds from property insurance recovery associated with property, plant and equipment	11,415		8,829
Proceeds from sales of property and equipment	307	112	99
Purchases of short-term investments	(10,032)	(10,014)	(30,009)
Proceeds from short-term investments	20,037	10,012	30,057
Proceeds from (deposits of) restricted cash			(1)
Proceeds from sales of carbon credits	761	2,597
Payments on contractual obligations-carbon credits	(786)	(2,266)
Other assets	(508)	(816)	(488)
Net cash used by continuing investing activities	(121,669)	(44,596)	(25,988)
Cash flows from continuing financing activities
Proceeds from revolving debt facility	209,238	669,739	540,098
Payments on revolving debt facility	(209,238)	(669,739)	(540,098)
Proceeds from secured term loan, net of fees		14,766
Proceeds from modification of secured term loan, net of fees		10,347
Proceeds from other long-term debt, net of fees			47
Payments associated with induced conversion of 5.5% convertible debentures		(558)
Acquisitions of 5.5% convertible debentures			(2,494)
Payments on other long-term debt	(7,019)	(15,345)	(8,909)
Payments on loans secured by cash value of life insurance policies	(1,918)	(84)	(380)
Payments of debt issuance costs	(88)	(112)
Proceeds from short-term financing	11,192	6,775	4,585
Payments on short-term financing	(7,584)	(4,950)	(3,781)
Proceeds from exercises of stock options	767	1,197	829
Purchase of treasury stock			(2,421)
Excess income tax benefit associated with stock-based compensation	498	1,160	185
Acquisition of redeemable preferred stock	(39)
Dividends paid on preferred stocks	(300)	(305)	(305)
Net cash provided (used) by continuing financing activities	(4,491)	12,891	(12,644)
Cash flows of discontinued operations:
Operating cash flows	(220)	(283)	(362)
Net increase (decrease) in cash and cash equivalents	(26,909)	57,983	5,207
Cash and cash equivalents at beginning of year	124,929	66,946	61,739
Cash and cash equivalents at end of year	98,020	124,929	66,946
Cash payments for:
Interest on long-term debt and other	4,325	6,547	6,954
Income taxes, net of refunds	21,766	49,129	11,373
Noncash investing and financing activities:
Insurance claims receivable associated with property, plant and equipment	546		171
Other assets, accounts payable, other liabilities, and long-term debt associated with additions of property, plant and equipment	15,522	6,289	5,420
Debt issuance costs incurred associated with secured term loan		839
Debt issuance costs written off associated with 5.5% debentures		353	58
Accrued liabilities extinguished associated with 5.5% debentures		349
5.5% debentures converted to common stock		$ 26,900