Debt (Details 2) (USD $)	1 Months Ended	3 Months Ended		12 Months Ended
	Apr. 30, 2007 Numerator Denominator	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2011	Dec. 31, 2010	Apr. 16, 2007
Debt
Loss on extinguishment of debt				$ 3,349,000
Components of interest expense recorded on the notes
Accretion of the discount on the Notes				1,260,000	3,058,000
Convertible Notes
Debt
Original conversion rate, number of shares to be issued per $1000 of principal amount of notes (in shares)	36.7277
Convertible debt principal amount, basis for exchange	1,000
Conversion price of convertible notes (in dollars per share)		$ 50.59	$ 45.95			$ 27.23
Premium over the closing market price of common stock on April 16, 2007 (as a percent)						38.00%
Principal of notes tendered for conversion			7,500,000
Notes tendered, cash paid		98,100,000	7,500,000
Notes tendered, shares issued upon conversion		1,660,095	111,318
Loss on extinguishment of debt		3,000,000	300,000
Components of interest expense recorded on the notes
Contractual interest				2,025,000	4,355,000
Accretion of the discount on the Notes				1,260,000	3,058,000
Total interest expense on the Notes				$ 3,285,000	$ 7,413,000
Effective interest rate (as a percent)				6.70%	7.00%