Notes Payable - Convertible (Details) (USD $)	12 Months Ended			1 Months Ended	3 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Jan. 31, 2013	Dec. 31, 2012	Sep. 28, 2012	Jul. 12, 2013	Jul. 11, 2013
Debt Instrument [Line Items]
Repayment of notes payable - convertible	$ 0	$ 246,797,000	$ 164,649,000
Equity component of convertible debt		93,450,000	41,486,000
Period after receipt of conversion notice of average daily closing price of company common stock	20 days
Repayments of Notes Payable	150,000,000	0	50,000,000
Common stock, shares issued	132,010,104	121,991,677
Amortization of notes payable discount	1,238,000	3,188,000	4,976,000
Interest Expense, Debt	0	8,038,000	21,184,000
Convertible Debt
Debt Instrument [Line Items]
Noncash interest charges		2,072,000	4,291,000
Contractual interest expense		5,400,000	15,744,000
Amortization of notes payable discount		566,000	1,149,000
2026 Notes
Debt Instrument [Line Items]
Interest Rate						3.95%
Repayment of notes payable - convertible					164,649,000
Settlement value					123,163,000
Outstanding principal balance			15,537,000		15,537,000
Repayments of Notes Payable				20,702,000
Adjustments to Additional Paid in Capital, Other				5,028,000
Interest Expense, Debt				137,000
2026 Notes | Convertible Debt
Debt Instrument [Line Items]
Equity component of convertible debt					41,486,000
2028 Notes
Debt Instrument [Line Items]
Interest Rate			5.125%		5.125%
Outstanding principal balance			223,035,000		223,035,000		222,905,000	130,000
Repayments of Notes Payable		226,427,000
Adjustments to Additional Paid in Capital, Other		3,197,000
Common stock, shares issued		2,407,911
Interest Expense, Debt		$ 195,000