Related Party Transactions - Additional Information (Detail) $ in Thousands	1 Months Ended		3 Months Ended		6 Months Ended	9 Months Ended		12 Months Ended
	Oct. 31, 2019 shares	Jan. 31, 2019 USD ($) shares	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2019 USD ($)	Sep. 30, 2019 USD ($) Investment shares	Sep. 30, 2018 USD ($) shares	Dec. 31, 2018 USD ($)
Related Party Transaction [Line Items]
Total components due to affiliates			$ 532,160			$ 532,160		$ 301,581
Management fee			29,858	$ 11,823		$ 69,522	$ 28,073
Stock repurchased | shares						14,655,000
Stock repurchased, value			55,870	19,489		$ 161,537	30,603
Recognized liabilities for Performance Participation expense			56,322	$ 12,447		106,383	$ 29,796
Portfolio company incentive compensation awards		$ 8,000						4,700
Amoritzation period of grant		4 years
Unrecognized compensation cost relating to portfolio company incentive compensation awards			6,500			$ 6,500
Unrecognized compensation cost recognition period						3 years 3 months 18 days
Class I Shares [Member]
Related Party Transaction [Line Items]
Stock issued as payment for services | shares		400,000
Stock repurchased | shares						8,367,000
Amoritzation period of grant						1 year
Adviser [Member]
Related Party Transaction [Line Items]
Percentage of management fee on NAV per annum						1.25%
Stock repurchased, value								3,400
Adviser [Member] | Other Assets [Member] | Jupiter 12 Industrial Portfolio [Member]
Related Party Transaction [Line Items]
Receivable from affiliates			2,900			$ 2,900
Special Limited Partner [Member] | Class I Shares [Member]
Related Party Transaction [Line Items]
Stock issued as payment for services | shares		3,500,000
Stock redeemed, shares | shares		400,000				2,800,000
Stock redeemed, value		$ 4,300				$ 31,100
Stock exchanged, shares | shares		1,100,000
LivCor L.L.C. [Member] | Other Assets [Member]
Related Party Transaction [Line Items]
Receivable from affiliates			3,600			3,600
LNLS [Member]
Related Party Transaction [Line Items]
Costs paid to LNLS for title services related to investments			4,700			$ 7,500
Number of Investments with Capitalized or Deferred Financing Costs | Investment						28
Accrued Stockholder Servicing Fee [Member]
Related Party Transaction [Line Items]
Total components due to affiliates			399,100			$ 399,100		238,496
Advanced Organization and Offering Costs [Member]
Related Party Transaction [Line Items]
Total components due to affiliates			6,647			6,647		8,181
Advanced Expenses [Member]
Related Party Transaction [Line Items]
Total components due to affiliates			1,700			1,700		1,100
Accrued Management Fee [Member]
Related Party Transaction [Line Items]
Total components due to affiliates			11,054			11,054		5,124
Accrued Management Fee [Member] | Adviser [Member]
Related Party Transaction [Line Items]
Total components due to affiliates			$ 11,100			$ 11,100		$ 5,100
Management Fee [Member] | Adviser [Member] | Class I Shares [Member]
Related Party Transaction [Line Items]
Stock issued as payment for services | shares						5,288,447	2,220,262
Stock repurchased | shares						6,614,229	700,298
Stock repurchased, value					$ 72,700		$ 7,600
Management Fee [Member] | Subsequent Event [Member] | Adviser [Member] | Class I Shares [Member]
Related Party Transaction [Line Items]
Stock issued as payment for services | shares	971,219