Interim Financial Information (Unaudited) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	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
Revenues	$ 138,899	$ 86,668	$ 99,270	$ 98,796	$ 103,364	$ 84,884	$ 92,830	$ 67,249	$ 423,633	$ 348,327	$ 239,909
Costs and Expenses	86,235	67,379	68,071	71,501	90,223	69,232	61,571	60,175	293,186	281,201	232,600
Income from operations	52,664	19,289	31,199	27,295	13,141	15,652	31,259	7,074	130,447	67,126	7,309
Net income (loss)	24,153	(2,247)	35,401	1,503	(7,341)	23,458	25,003	(14,509)	58,810	26,611	(8,468)
Basic earnings (loss) per share	$ 0.62	$ (0.06)	$ 0.90	$ 0.04	$ (0.19)	$ 0.59	$ 0.62	$ (0.36)	$ 1.50	$ 0.66	$ (0.21)
Diluted earnings (loss) per share	$ 0.61	$ (0.06)	$ 0.90	$ 0.04	$ (0.19)	$ 0.58	$ 0.62	$ (0.36)	$ 1.50	$ 0.66	$ (0.21)
Gains Losses On Extinguishment Of Debt								2,400		(2,377)	(5,627)
Parent Company [Member]
Revenues									333,901	260,574	186,184
Costs and Expenses									232,029	217,630	173,030
Income from operations									101,872	42,944	13,154
Net income (loss)									58,810	26,611	(8,468)
Gains Losses On Extinguishment Of Debt										$ (2,377)	$ (5,627)