Income Taxes (Details 2) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Current income tax expense:
Federal	$ 15,039,000	$ 5,850,000	$ 6,525,000
State	2,539,000	1,805,000	1,547,000
Total current	17,578,000	7,655,000	8,072,000
Deferred income tax (benefit) expense:
Federal	(4,732,000)	(3,870,000)	(43,409,000)
State	803,000	(596,000)	(6,679,000)
Total deferred	(3,929,000)	(4,466,000)	(50,088,000)
Total provision for income tax	13,649,000	3,189,000	(42,016,000)
Income Tax
Income before provision for income tax	119,894,000	34,291,000	(155,370,000)
Federal statutory income tax rate (as a percent)	35.00%	35.00%	35.00%
Federal income tax at statutory rate	1,335,000	(2,842,000)	(39,377,000)
Permanent items	36,000	20,000	1,000
State income taxes net of federal benefit	2,844,000	1,027,000	(5,625,000)
Current year change in valuation allowance	(64,000)	(1,022,000)	1,562,000
Prior period adjustments and tax rate changes	163,000	70,000	1,497,000
Provision on income from Class A units	9,323,000	5,753,000	(525,000)
Write-off of deferred income tax assets			293,000
Other	12,000	183,000	158,000
Provision for income tax	13,649,000	3,189,000	(42,016,000)
Current deferred tax assets
Accruals and reserves	78,000	64,000
Derivative instruments	14,807,000	16,031,000
Current deferred tax assets	14,885,000	16,095,000
Current deferred tax liabilities
Derivative instruments		16,000
Current subtotal	14,885,000	16,079,000
Long-term deferred tax assets
Accruals and reserves	48,000	34,000
Derivative instruments	20,301,000	14,241,000
Phantom unit compensation	2,103,000	1,684,000
Capital loss carryforward	971,000	975,000
State net operating loss carryforward	101,000	156,000
Long-term deferred tax assets	23,524,000	17,090,000
Valuation allowance	(977,000)	(1,036,000)
Net long-term deferred tax assets	22,547,000	16,054,000
Long-term deferred tax liabilities
Property, plant and equipment and intangibles	2,123,000	3,529,000
Phantom unit compensation		31,000
Investment in affiliated groups	114,088,000	100,345,000
Derivative instruments		30,000
Long-term deferred tax liabilities	116,211,000	103,935,000
Long-term subtotal	(93,664,000)	(87,881,000)
Net deferred tax liabilitiy	(78,779,000)	(71,802,000)
Corporation
Deferred income tax (benefit) expense:
Total provision for income tax	10,907,000	1,890,000	(40,577,000)
Income Tax
Income before provision for income tax	3,813,000	(8,120,000)	(112,506,000)
Federal statutory income tax rate (as a percent)	35.00%	35.00%	35.00%
Federal income tax at statutory rate	1,335,000	(2,842,000)	(39,377,000)
Permanent items	36,000	20,000	1,000
State income taxes net of federal benefit	102,000	(272,000)	(4,186,000)
Current year change in valuation allowance	(64,000)	(1,022,000)	1,562,000
Prior period adjustments and tax rate changes	163,000	70,000	1,497,000
Provision on income from Class A units	9,323,000	5,753,000	(525,000)
Write-off of deferred income tax assets			293,000
Other	12,000	183,000
Provision for income tax	10,907,000	1,890,000	(40,577,000)
Long-term deferred tax liabilities
State net operating loss carryforwards	100,000
Valuation allowance as a percentage of long-term deferred tax asset attributable to state net operating losses	100.00%
Capital loss carryforward	1,000,000
Valuation allowance as a percentage of long-term deferred tax asset attributable to capital loss carryforwards	100.00%
Partnership
Deferred income tax (benefit) expense:
Total provision for income tax	2,742,000	1,299,000	(1,439,000)
Income Tax
Income before provision for income tax	124,087,000	47,761,000	(32,800,000)
Federal statutory income tax rate (as a percent)	0.00%	0.00%	0.00%
State income taxes net of federal benefit	2,742,000	1,299,000	(1,439,000)
Provision for income tax	2,742,000	1,299,000	(1,439,000)
Eliminations
Income Tax
Income before provision for income tax	$ (8,006,000)	$ (5,350,000)	$ (10,064,000)
Federal statutory income tax rate (as a percent)	0.00%	0.00%	0.00%