Debt Including Capital Lease Obligations - 4.25% Convertible Senior Notes (Details) (USD $)	3 Months Ended
	Mar. 31, 2014		Mar. 31, 2013		Dec. 31, 2013
Interest Expense, Debt [Abstract]
Amortization of discount on the debt component	$ 2,956,000		$ 2,619,000
4.25% Convertible Senior Notes
Debt Instrument [Line Items]
Stated interest rate on debt instrument	4.25%		4.25%		4.25%
Conversion rate of debt into equity	0.0445524000
Conversion price (in dollars per share)	$ 22.45				$ 22.45
Principal amount of debt component	200,000,000	[1]	200,000,000	[1]	200,000,000	[1]
Unamortized discount	(32,994,000)		(44,299,000)		(35,950,000)
Net carrying amount of debt component	167,006,000		155,701,000		164,050,000
Equity component	84,904,000		84,904,000		84,904,000
Issuance costs and income taxes	(3,210,000)		(3,210,000)		(3,210,000)
Equity component, net of issuance costs and income taxes	81,694,000		81,694,000		81,694,000
Interest Expense, Debt [Abstract]
4.25% coupon interest	2,125,000		2,125,000
Amortization of deferred financing fees	117,000		117,000
Amortization of discount on the debt component	2,956,000		2,619,000
Total interest expense related to the Convertible Notes	$ 5,198,000		$ 4,861,000

[1] As of March 31, 2014, December 31, 2013 and March 31, 2013, the Convertible Notes' "if-converted" value did not exceed their principal amount because our common stock price was below the conversion price of the Convertible Notes.