Notes Payable - Convertible (Details) - USD ($)	1 Months Ended	3 Months Ended	12 Months Ended
	Jan. 31, 2013	Dec. 31, 2012	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Jul. 12, 2013	Jul. 11, 2013	Sep. 28, 2012
Debt Instrument [Line Items]
Repayment of notes payable - convertible			$ 0	$ 0	$ 246,797,000
Equity component of convertible debt					93,450,000
Repayments of notes payable			$ 150,000,000	$ 150,000,000	0
Common stock, shares issued			141,007,725	132,010,104
Amortization of notes payable discount			$ 1,306,000	$ 1,238,000	3,188,000
Interest Expense, Debt					8,038,000
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
Repayments of notes payable	$ 20,702,000
Decrease to additional paid in capital	5,028,000
Interest Expense, Debt	$ 137,000		$ 0	0
2028 Notes
Debt Instrument [Line Items]
Interest Rate		5.125%
Outstanding principal balance		$ 223,035,000				$ 222,905,000	$ 130,000
Repayments of notes payable					226,427,000
Decrease to additional paid in capital					$ 3,197,000
Period after receipt of conversion notice of average daily closing price of company common stock			20 days
Common stock, shares issued					2,407,911
Interest Expense, Debt			$ 0	$ 0	$ 195,000
Convertible Debt
Debt Instrument [Line Items]
Noncash interest charges					2,072,000
Contractual interest expense					5,400,000
Amortization of notes payable discount					$ 566,000
Convertible Debt | 2026 Notes
Debt Instrument [Line Items]
Equity component of convertible debt		$ 41,486,000