Senior secured notes, convertible notes, and corporate debt, net (Details)				9 Months Ended
	Jul. 22, 2019 USD ($)	Apr. 27, 2018 USD ($)	Aug. 09, 2017 USD ($) $ / shares	Sep. 30, 2019 USD ($) D item	Sep. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)	Jan. 30, 2018 USD ($)	Dec. 31, 2017 USD ($)
Senior secured notes, Convertible notes, and Corporate debt
Unamortized deferred financing costs				$ (1,660,000)		$ (2,564,000)
Total Senior secured notes, net				179,189,000		178,870,000
Total Senior unsecured notes, net				104,441,000		48,457,000
Total Convertible notes, net				110,773,000		$ 109,979,000
Total carrying amount of debt components				394,403,000
Total carrying amount of conversion option of equity components recorded in additional paid-in capital				1,538,000
Proceeds from Issuance of Secured Debt					$ 41,328,000
Contractual maturities of the Senior Secured Notes, Convertible Notes, and Corporate debt
2021				104,441,000
2022				179,189,000
2023				110,773,000
Long-term Debt, Total				394,403,000
Senior Secured Notes
Senior secured notes, Convertible notes, and Corporate debt
Debt instrument, face value				$ 180,000,000
Interest rate (as a percent)				7.50%
Unamortized premium - Senior secured notes				$ 1,852,000
Unamortized deferred financing costs				(2,663,000)
Total Senior secured notes, net				179,189,000
Convertible Notes
Senior secured notes, Convertible notes, and Corporate debt
Debt instrument, face value			$ 115,000,000	$ 115,000,000
Interest rate (as a percent)			7.00%	7.00%
Conversion ratio			1.4997
Principal amount of notes for conversion			$ 25
Initial conversion price | $ / shares			$ 16.67
Principal amount of the notes to be redeemed (as a percent)			100.00%
Threshold period of specified consecutive trading days within which common stock price to conversion price of convertible debt instruments must exceed threshold percentage for a specified number of trading days to trigger conversion feature | D				30
Threshold period of specified consecutive trading days within which the common stock price, used in a calculation with with the conversion rate, the result of which must exceed the threshold percentage				5 days
Specified period of time used to calculate average closing market price of common stock to be used as a factor in determining potential trigger of conversion feature				10 days
Gross carrying value of convertible notes			$ 112,700,000
Gross carrying value of the equity component			$ 2,300,000
Unamortized discount - Convertible notes				$ (1,538,000)
Unamortized deferred financing costs				(2,689,000)
Total Convertible notes, net				$ 110,773,000
Convertible Notes | Minimum
Senior secured notes, Convertible notes, and Corporate debt
Percentage of common stock price to conversion price of convertible debt instruments to determine eligibility of conversion				120.00%
Threshold number of specified trading days that common stock price to conversion price of convertible debt instruments must exceed threshold percentage within a specified consecutive trading period to trigger conversion feature | item				20
The threshold percentage that per share value of distributions exceeds the average market price which may trigger the conversion feature				10.00%
Convertible Notes | Maximum
Senior secured notes, Convertible notes, and Corporate debt
Threshold percentage of the trading price of the convertible debt instrument to the product of the conversion rate and the closing stock price during any five consecutive trading day period				98.00%
Corporate Debt
Senior secured notes, Convertible notes, and Corporate debt
Unamortized deferred financing costs				$ (3,059,000)
Total Convertible notes, net				104,441,000
6.50% Senior Notes due 2021
Senior secured notes, Convertible notes, and Corporate debt
Debt instrument, face value		$ 50,000,000		$ 50,000,000
Interest rate (as a percent)		6.50%		6.50%
Principal amount of the notes to be redeemed (as a percent)		101.00%
6.50% Senior Notes due 2021 | On or after April 30, 2019 and before April 30, 2020
Senior secured notes, Convertible notes, and Corporate debt
Principal amount of the notes to be redeemed (as a percent)		101.00%
6.50% Senior Notes due 2021 | On or after April 30, 2020
Senior secured notes, Convertible notes, and Corporate debt
Principal amount of the notes to be redeemed (as a percent)		100.00%
6.20% Senior Notes due 2026
Senior secured notes, Convertible notes, and Corporate debt
Debt instrument, face value	$ 57,500,000			$ 57,500,000
Interest rate (as a percent)	6.20%			6.20%
Principal amount of the notes to be redeemed (as a percent)	101.00%
Proceeds from Issuance of Secured Debt	$ 55,300,000
6.20% Senior Notes due 2026 | On or after July 30, 2022 and before July 30, 2025
Senior secured notes, Convertible notes, and Corporate debt
Principal amount of the notes to be redeemed (as a percent)	101.00%
6.20% Senior Notes due 2026 | On or after July 30, 2025
Senior secured notes, Convertible notes, and Corporate debt
Principal amount of the notes to be redeemed (as a percent)	100.00%
6.20% Senior Notes due 2026 | Over-allotment option
Senior secured notes, Convertible notes, and Corporate debt
Debt instrument, face value	$ 7,500,000
ReadyCap Holdings LLC | Senior Secured Notes
Senior secured notes, Convertible notes, and Corporate debt
Debt instrument, face value							$ 40,000,000	$ 140,000,000
Interest rate (as a percent)							7.50%	7.50%
Yield-to-maturity (as a percent)							6.50%