Convertible Debentures and Credit Arrangements (Details) - USD ($)		1 Months Ended	12 Months Ended
	May 15, 2018	May 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	May 31, 2018	Apr. 30, 2018	Nov. 30, 2012
Debt Instrument [Line Items]
Debt Instrument, Gain (Loss) from Covenant Liability			$ (4,500,000)
Credit facility - current			22,100,000	$ 0
Proceeds from credit facility			35,000,000	50,000,000
Long-term Debt			68,600,000
Interest payments			11,100,000		$ 5,000,000
Amortization of debt discount			4,513,000	2,542,000
Line of Credit [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity		$ 75,000,000				$ 100,000,000
Convertible Debt [Member]
Debt Instrument [Line Items]
Interest rate on debentures								5.25%
Outstanding debentures			41,000,000
Long-term Debt			$ 41,000,000
Debt instrument effective rate			8.70%
Debt Instrument, Face Amount			$ 41,000,000					$ 55,000,000.0
Debt Instrument, Repurchased Face Amount				14,000,000
Repayments of Long-term Debt				14,500,000
Stock Issued During Period, Value, Conversion of Convertible Securities, Net of Adjustments				800,000
Gain (Loss) on Extinguishment of Debt				(29,000)
Debt Instrument Option Common Stock Closing Sales Price Number Of Trading Days			20 days
Debt Instrument Option Number Of Consecutive Trading Days			30 days
Debt Instrument Option Number Of Consecutive Trading Days In Which Trading Price Per Thousand Principal Amount Was Less Than Specified Criteria			5 days
Debt Instrument Option Number Of Consecutive Trading Days During Which Trading Price Per Thousand Principal Amount Was Less Than Specified Percentage			5 days
Principal Amount Convertible Debenture			$ 1,000
Debt Instrument Option Common Stock Closing Sales Price As Percentage Of Conversion Price			98.00%
Debt Conversion, Converted Instrument, Shares Issued			55.17
Debt Instrument, Convertible, Conversion Price			$ 18.13
Share Price			$ 11.20
Percentage Threshold Closing Sale Price Of Common Stock Higher Than Conversion Price			140.00%
Debt Instrument Cash Redemption Price			100.00%
Redemption Rate Of Debt Instrument Demanded By Holder Under Change In Business Control			50.00%
Percentage Of Principal Amount And Accrued And Unpaid Interest For Repurchase Of Debt			100.00%
Debt Instrument, Fair Value Disclosure			$ 41,600,000
Debt Instrument, Convertible, Carrying Amount of Equity Component			5,600,000
Debt Instrument, Unamortized Discount			500,000
Debt Instrument, Convertible Principal Amount Outstanding			40,500,000
Amortization of debt discount			$ 500,000	1,500,000
Convertible Debt [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument Common Stock Closing Sales Price As Percentage Of Conversion Price			130.00%
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity		75,000,000				100,000,000
Debt Instrument, Debt Covenants, Cash and Cash Equivalent Threshold						50,000,000
Liquidity threshold						20,000,000
Minimum aggregate appraised value plus liquidity threshold						350,000,000
Debt Instrument, Debt Covenant, Expense Threshold						11,500,000
Outstanding debentures						68,600,000
Revolving Credit Facility [Member] | Line of Credit [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity		75,000,000				15,000,000
Debt Instrument, Debt Covenants, Cash and Cash Equivalent Threshold			$ 50,000,000			$ 50,000,000
Line of Credit Facility, Repayment Feature, Noncurrent			500,000
Debt Instrument, Debt Covenant, Cash and Cash Equivalent Threshold, Interest and Prepayment Fee, Percent						100.00%
Long-term line of credit		50,000,000				$ 35,000,000	$ 50,000,000
Proceeds from credit facility	$ 32,700,000	$ 44,300,000
Repayments of Debt	$ 41,000,000
Debt instrument, term		3 years
Amount outstanding threshold		$ 50,000,000
Commitment fee percentage		0.75%
Liquidity threshold		$ 20,000,000
Minimum aggregate appraised value plus liquidity threshold						350,000,000
Debt Instrument, Debt Covenant, Deployment Threshold						40,000,000
Debt Instrument, Debt Covenant, Expense Threshold						11,500,000
Outstanding debentures			68,600,000
Unamortized discount (premium) and debt issuance costs, net			3,500,000
Long-term Debt			65,100,000
Amortization of debt issuance costs			$ 14,600,000	4,400,000
Debt instrument effective rate			15.20%
Interest payments			$ 10,000,000	$ 2,500,000
Revolving Credit Facility [Member] | Line of Credit [Member] | Application A [Member] | London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Basis spread on variable rate		8.50%
Revolving Credit Facility [Member] | Line of Credit [Member] | Application A [Member] | London Interbank Offered Rate (LIBOR) [Member] | Minimum [Member]
Debt Instrument [Line Items]
Basis spread on variable rate		1.00%
Revolving Credit Facility [Member] | Line of Credit [Member] | Application B [Member]
Debt Instrument [Line Items]
Basis spread on variable rate		2.00%
Interest rate on debentures		7.50%
Revolving Credit Facility [Member] | Line of Credit [Member] | Application B [Member] | London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Basis spread on variable rate		1.00%
Revolving Credit Facility [Member] | Line of Credit [Member] | Application B [Member] | Federal Funds Effective Swap Rate [Member]
Debt Instrument [Line Items]
Basis spread on variable rate		0.50%
Term Loans [Member] | Line of Credit [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity						$ 85,000,000