Credit Facility and Convertible Debentures - Additional Information (Detail) - USD ($)		1 Months Ended	3 Months Ended
	Apr. 15, 2019	May 31, 2017	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018	May 31, 2018
Debt Instrument [Line Items]
Gain (loss) from covenant liability			$ (2,000,000)
Interest expense			2,535,000	$ 2,690,000
Revolving Credit Facility
Debt Instrument [Line Items]
Cash and cash equivalent threshold						$ 50,000,000
Liquidity threshold						20,000,000
Minimum aggregate appraised value plus liquidity threshold						350,000,000
Expense threshold						11,500,000
Revolving Credit Facility | Line of Credit
Debt Instrument [Line Items]
Interest expense			$ 2,500,000	1,800,000
Debt instrument, interest rate, effective percentage			15.30%
Interest paid			$ 1,900,000	1,300,000
Credit Facility | Revolving Credit Facility | Interest Rate Application A | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Basis spread on variable rate		8.50%
Credit Facility | Revolving Credit Facility | Interest Rate Application A | London Interbank Offered Rate (LIBOR) | Minimum
Debt Instrument [Line Items]
Basis spread on variable rate		1.00%
Credit Facility | Revolving Credit Facility | Interest Rate Application B
Debt Instrument [Line Items]
Basis spread on variable rate		2.00%
Credit Facility | Revolving Credit Facility | Interest Rate Application B | Minimum
Debt Instrument [Line Items]
Basis spread on variable rate		7.50%
Credit Facility | Revolving Credit Facility | Interest Rate Application B | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Basis spread on variable rate		1.00%
Credit Facility | Revolving Credit Facility | Interest Rate Application B | Federal Funds Effective Swap Rate
Debt Instrument [Line Items]
Basis spread on variable rate		0.50%
Amended Credit Facility
Debt Instrument [Line Items]
Long-term line of credit outstanding			68,600,000
Cash and cash equivalent threshold			50,000,000			50,000,000
Liquidity threshold						20,000,000
Minimum aggregate appraised value plus liquidity threshold						350,000,000
Deployment threshold						40,000,000.0
Expense threshold						11,500,000.0
Unamortized discount and debt issuance costs			2,900,000
Long-term debt			65,700,000
Credit facility repayment feature			$ 7,100,000		$ 2,000,000	$ 500,000
Amended Credit Facility | Subsequent Event
Debt Instrument [Line Items]
Repayments of lines of credit	$ 24,000,000
Periodic payment, interest	$ 2,900,000
2018 Debentures | Convertible Debt
Debt Instrument [Line Items]
Interest expense				$ 900,000