Credit Facilities (5.00% Convertible Senior Notes due 2024) (Details)			3 Months Ended	6 Months Ended
	Apr. 03, 2019 USD ($) day $ / shares	Nov. 02, 2015 USD ($) $ / shares	Jun. 30, 2019 USD ($) shares	Jun. 30, 2019 USD ($) day	Mar. 31, 2019	Dec. 31, 2018 USD ($)	Aug. 09, 2018 USD ($)
Line of Credit Facility [Line Items]
Stock trigger price (usd per share) | $ / shares	$ 6.61
Maximum equity owned by Investor			9.50%	9.50%
Carrying value			$ 165,024,000	$ 165,024,000		$ 198,078,000
Convertible notes
Line of Credit Facility [Line Items]
Carrying value			36,096,000	36,096,000		$ 75,917,000
Debt, Conversion Option			41,200,000	41,200,000
5% Note | Convertible notes
Line of Credit Facility [Line Items]
Debt instrument, stated interest rate	5.00%				5.00%
Maximum conversion amount	30.00%
Limit on conversion	30.00%
Debt instrument face amount	$ 25,000,000.0
Convertible debt, conversion ratio	0.15129
Debt Instrument, Convertible, Face Amount Of Each Note That Is Convertible	$ 1.00
Mandatory conversion of shares	$ 1,666,666
Convertible debt redemption, consecutive trading days threshold | day	5
Carrying value			67,200,000	67,200,000
Debt Issuance Costs, Line of Credit Arrangements, Gross			1,200,000	1,200,000
Deferred financing cost			500,000	500,000
Reduction in Equity	$ 700,000
Debt Conversion, Converted Instrument, Amount			1,700,000
Debt Conversion, Converted Amount, Carrying Value			700,000	700,000
Debt Conversion, Accrued Interest			$ 0	0
Debt Conversion, Converted Instrument, Shares Issued | shares			254,565
Convertible notes payable			$ 25,800,000	25,800,000
Debt issuance costs, gross			500,000	500,000
Voluntary Conversion
Line of Credit Facility [Line Items]
Stock trigger price (usd per share) | $ / shares	$ 7.271
Voluntary Conversion | Convertible notes
Line of Credit Facility [Line Items]
Conversion price | $ / shares	$ 8.2624
Convertible debt, conversion ratio	0.12103
Debt Instrument, Convertible, Face Amount Of Each Note That Is Convertible	$ 1.00
Convertible Senior Notes Due 2020
Line of Credit Facility [Line Items]
Debt instrument, stated interest rate							3.25%
Debt instrument face amount							$ 40,500,000.0
Convertible Senior Notes Due 2020 | Convertible notes
Line of Credit Facility [Line Items]
Debt instrument, stated interest rate		3.25%
Periodic payment, principal				$ 0
Conversion price | $ / shares		$ 111.82
Debt instrument face amount		$ 125,000,000
Convertible debt, conversion ratio		8.9431
Convertible debt redemption, consecutive trading days threshold | day				30
Convertible notes payable			10,400,000	$ 10,400,000
Debt issuance costs, gross			$ 100,000	100,000
Two Investors | 5% Note | Convertible notes
Line of Credit Facility [Line Items]
Debt instrument face amount	42,000,000.0
Two Investors | 5% Note | Face Value Per Note
Line of Credit Facility [Line Items]
Debt instrument face amount	900
Two Investors | Convertible Senior Notes Due 2020 | Face Value Per Note
Line of Credit Facility [Line Items]
Debt instrument face amount	$ 1,000
Minimum | 5% Note | Convertible notes
Line of Credit Facility [Line Items]
Periodic payment, interest				4,600,000
Minimum | Convertible Senior Notes Due 2020 | Convertible notes
Line of Credit Facility [Line Items]
Periodic payment, interest				700,000
Maximum | 5% Note | Convertible notes
Line of Credit Facility [Line Items]
Periodic payment, interest				15,500,000
Maximum | Convertible Senior Notes Due 2020 | Convertible notes
Line of Credit Facility [Line Items]
Periodic payment, interest				$ 800,000