Selected Quarterly Results (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	Dec. 31, 2009
Effect of Fourth Quarter Events [Line Items]
Patent Sale Expense									$ 16,500,000
Other Tax Expense (Benefit)	4,500,000				1,500,000	6,800,000				8,300,000		16,400,000
REVENUES	87,877,000	434,010,000	71,871,000	69,305,000	76,956,000	76,455,000	69,873,000	78,458,000	663,063,000	301,742,000	394,545,000
NET INCOME	$ 15,532,000	$ 235,669,000	$ 9,673,000	$ 10,930,000	$ 22,767,000	$ 26,206,000	$ 17,156,000	$ 23,339,000	$ 271,804,000	$ 89,468,000	$ 153,616,000
NET INCOME PER COMMON SHARE — BASIC	$ 0.38	$ 5.61	$ 0.22	$ 0.24	$ 0.50	$ 0.58	$ 0.38	$ 0.52	$ 6.31	$ 1.97	$ 3.48
NET INCOME PER COMMON SHARE — DILUTED	$ 0.38	$ 5.56	$ 0.22	$ 0.24	$ 0.49	$ 0.57	$ 0.37	$ 0.51	$ 6.26	$ 1.94	$ 3.43