Debt Convertible Notes (Details) - USD ($)		9 Months Ended	12 Months Ended
	Oct. 06, 2017	Sep. 30, 2017	Dec. 31, 2016	Dec. 31, 2014	Dec. 31, 2017	Dec. 08, 2014
Debt Instrument [Line Items]
Senior Credit Facility, applicable margin		3.25%
Long-term debt		$ 148,469,000	$ 144,340,000
Convertible Debt [Member] | Senior 3 Point 25 Percent Convertible Notes Due 2020 [Member]
Debt Instrument [Line Items]
Senior Credit Facility, applicable margin		3.25%
Principal amount of Convertible Senior Notes outstanding		$ 167,314,000	167,314,000
Unamortized discount of liability component		(16,587,000)	(20,221,000)
Unamortized debt issuance costs				$ (4,200,000)
Net carrying amount of liability component		148,469,000	144,340,000
Less: current portion		0	0
Long-term debt		148,469,000	144,340,000
Carrying value of equity component, net of issuance costs		29,211,000	29,211,000			$ 30,700,000
Fair value of outstanding Convertible Senior Notes		$ 253,765,000	$ 165,223,000
Remaining amortization period of discount on the liability component		3 years 3 months	4 years	6 years
Other Current Assets [Member] | Convertible Debt [Member] | Senior 3 Point 25 Percent Convertible Notes Due 2020 [Member]
Debt Instrument [Line Items]
Unamortized debt issuance costs		$ (2,258,000)	$ (2,753,000)
Subsequent Event [Member]
Debt Instrument [Line Items]
Applicable base loan rate	1.50%				2.50%
Debt Instrument, Interest Rate, Stated Percentage, Initial Applicable Base Loan Rate	2.50%
Line of Credit Facility, Commitment Fee Percentage	0.10%
Line of credit facility, maximum borrowing capacity	$ 25,000,000.0
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage	0.50%