Condensed Consolidated Statements Of Cash Flows (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 5,720	$ 21,970
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, depletion and amortization	20,790	20,847
Accretion on asset retirement obligations	1,178	870
Accretion on interest-free debt	57	109
Amortization of deferred revenue	(654)	(572)
Amortization of advance royalties	60	126
Amortization of debt issuance costs	611	537
Amortization of actuarial gain	(72)	(148)
Equity in net (income)/loss of unconsolidated affiliates	3,449	(4,391)
Distribution from unconsolidated affiliate		2,958
Loss on retirement of advance royalties	32
(Gain) on sale/disposal of assets-net	(9,692)	(990)
Equity-based compensation	377	450
Changes in assets and liabilities:
Accounts receivable	6,316	2,650
Inventories	2,513	(8,172)
Advance royalties	(849)	(577)
Prepaid expenses and other assets	(2,261)	(176)
Accounts payable	377	(7,337)
Accrued expenses and other liabilities	1,373	5,698
Asset retirement obligations	(467)	(754)
Postretirement benefits	206	255
Net cash provided by operating activities	29,064	33,353
CASH FLOWS FROM INVESTING ACTIVITIES:
Additions to property, plant, and equipment	(17,060)	(42,387)
Proceeds from sales of property, plant, and equipment	11,224	1,290
Changes in restricted cash	1,079
Principal payments received on notes receivable		8,160
Cash paid from issuance of notes receivable		(8,160)
Investment in unconsolidated affiliates	(803)	(114)
Net cash used in investing activities	(5,560)	(41,211)
CASH FLOWS FROM FINANCING ACTIVITIES:
Borrowings on line of credit	80,550	133,250
Repayments on line of credit	(86,960)	(99,150)
Proceeds from issuance of long-term debt		2,603
Repayments on long-term debt	(1,822)	(1,233)
Distributions to unitholders	(14,268)	(27,202)
General partner's contributions	6	7
Net settlement of employee withholding taxes on unit awards vested	(53)	(85)
Payments on debt issuance costs	(980)
Payment of offering costs		(7)
Net cash (used in)/provided by financing activities	(23,527)	8,183
NET INCREASE IN CASH AND CASH EQUIVALENTS	(23)	325
CASH AND CASH EQUIVALENTS-Beginning of period	461	449
CASH AND CASH EQUIVALENTS-End of period	$ 438	$ 774