Debt (Details) (USD $)	3 Months Ended				9 Months Ended
	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Sep. 30, 2010	Sep. 30, 2011 denominator numerator	Sep. 30, 2010	Dec. 31, 2010	Apr. 16, 2007
Debt
Loss on extinguishment of debt related to the unamortized debt discount					$ 3,349,000
Components of interest expense recorded on the notes
Accretion of the discount on the Notes					1,260,000	2,269,000
Convertible Notes
Debt
Original conversion rate, number of shares to be issued per $1000 of principal amount of notes					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%				38.00%
Principal of notes tendered for conversion		98,100,000	7,500,000
Notes tendered, cash paid		98,100,000	7,500,000
Notes tendered, shares issued upon conversion (in shares)		1,660,095	111,318
Loss on extinguishment of debt related to the unamortized debt discount		3,000,000	300,000
Components of interest expense recorded on the notes
Contractual interest				1,089,000	2,025,000	3,268,000
Accretion of the discount on the Notes				769,000	1,260,000	2,269,000
Total interest expense on the Notes				1,858,000	3,285,000	5,537,000
Effective interest rate (as a percent)	0.00%			7.00%	6.70%	7.00%
Carrying amount of the liability and equity components of the notes
Carrying amount of the equity component							16,318,000
Principal balance of the liability component							105,574,000
Less: unamortized discount							4,436,000
Net carrying value of the liability component							101,138,000
Mortgage Payable
Carrying amount of the liability and equity components of the notes
Principal balance of the liability component	2,700,000				2,700,000
Fair value of debt instrument	$ 2,900,000				$ 2,900,000
Annual interest rate accrued on mortgage (as a percent)	7.91%				7.91%