Long-Term Obligations (Details) (USD $) Share data in Millions, except Per Share data, unless otherwise specified	3 Months Ended	9 Months Ended	1 Months Ended	9 Months Ended			0 Months Ended	1 Months Ended	9 Months Ended	1 Months Ended	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2012	Aug. 31, 2012 2 3/4 percent Convertible Senior Notes due 2019	Sep. 30, 2012 2 3/4 percent Convertible Senior Notes due 2019	Sep. 30, 2012 2 3/4 percent Convertible Senior Notes due 2019 On or after October 5, 2016 day	Sep. 30, 2012 2 3/4 percent Convertible Senior Notes due 2019 On or after July 1, 2019	Aug. 13, 2012 2 5/8 percent convertible subordinated notes due 2027	Sep. 30, 2012 2 5/8 percent convertible subordinated notes due 2027	Sep. 30, 2012 2 5/8 percent convertible subordinated notes due 2027	Jun. 30, 2012 Equipment Financing Arrangement	Sep. 30, 2012 Equipment Financing Arrangement	Dec. 31, 2011 Equipment Financing Arrangement	Sep. 30, 2012 Equipment Financing Arrangement Minimum	Sep. 30, 2012 Equipment Financing Arrangement Maximum
Long-term obligations
Debt issued			$ 201,300,000
Interest rate on convertible debt (as a percent)				2.75%				2.625%	2.625%
Proceeds raised net of issuance cost		194,689,000	194,700,000
Issuance costs			6,600,000
Debt discount, amortization period				7 years
Number of shares to be exchanged for convertible notes						12.1
Conversion price (in dollars per share)						$ 16.63
Within 30 consecutive trading days, number of days with closing price of the entity's common stock at least 130% of the conversion price to trigger the conversion option					20
Number of consecutive trading days during which a closing price of the entity's common stock of at least 130% of the conversion price for at least 20 days triggers the conversion option					30
Closing price of the entity's common stock as percentage of the conversion price, used as threshold for conversion eligibility conditions					130.00%
Ratio of additional redemption price of debt instrument to principal amount					0.09
Redemption price as a percentage of principal					100.00%		100.75%
Debt issuance costs, amortization period				7 years
Non-cash interest expense related to the amortization of the debt discount and debt issuance costs				894,000
Nonconvertible debt borrowing rate (as a percent)				8.00%
Amount of debt redeemed								162,500,000	162,500,000
Amount of debt redeemed including accrued interest		163,718,000						164,000,000
Loss on redemption of debt	4,770,000	4,770,000						4,800,000
Write-off of unamortized debt discount and debt issuance cost									3,600,000
Early redemption premium									1,200,000
Principal amount of convertible notes				12,100,000
Accrued interest payable on the notes				162,500,000
Basis for variable interest rate											three-year interest rate swap
Percentage added to variable rate basis													3.50%	4.00%
Additional principal amount drawn during the period										9,100,000
Principal drawn down under loan agreement											27,400,000
Interest rate on new draw down (as a percent)										4.12%
Weighted average interest rate (as a percent)											5.51%
Total											11,300,000	5,300,000
Maximum borrowing capacity for equipment purchases											$ 6,000,000