Summary Unaudited Quarterly Financial Information (Details) (USD $)	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Summary of the unaudited quarterly results of operations for the period
Revenue	$ 374,825,000	$ 425,681,000	$ 343,183,000	$ 372,903,000	$ 402,487,000	$ 406,950,000	$ 387,679,000	$ 356,545,000	$ 1,516,772,000	$ 1,553,661,000	$ 1,370,761,000
Operating income	54,482,000	81,634,000	58,722,000	47,027,000	63,984,000	60,173,000	74,706,000	53,882,000	241,866,000	252,743,000	211,875,000
Net income	28,163,000	85,260,000	33,678,000	26,618,000	43,819,000	24,611,000	94,594,000	26,773,000	173,720,000	189,797,000	117,197,000
Income (loss) per common share from continuing operations attributable to the controlling interest:
Basic (in dollars per share)	$ 0.47	$ 1.42	$ 0.56	$ 0.44	$ 0.73	$ 0.41	$ 1.58	$ 0.45
Diluted (in dollars per share)	$ 0.46	$ 1.39	$ 0.55	$ 0.44	$ 0.72	$ 0.41	$ 1.56	$ 0.44
Depreciation and depletion expense									(13,189,000)	(12,469,000)	(12,499,000)
Amount charged to non-operating income for increase in Tax Receivable Agreement liability							42,700,000		(29,000,000)	19,854,000	19,669,000
Adjustments to the net value of deferred tax assets recorded through income tax benefit						32,900,000	15,400,000
Amount of deferred tax assets expected to be realized							78,200,000
Benefit to non-operating income due to decrease in Tax Receivable Agreement liability						22,900,000
Decrease in Tax Receivable Agreement liability credited to additional paid-in-capital						$ 29,900,000