Related Party Transactions - Additional Information (Detail)	1 Months Ended			3 Months Ended		9 Months Ended		12 Months Ended
	Oct. 31, 2020 shares	Jan. 31, 2020 USD ($) shares	Jan. 31, 2019 USD ($)	Sep. 30, 2020 USD ($) shares	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) Investment shares	Sep. 30, 2019 USD ($) shares	Dec. 31, 2019 USD ($)
Related Party Transaction [Line Items]
Total components due to affiliates				$ 623,036,000		$ 623,036,000		$ 690,143,000
Management fee				$ 57,619,000	$ 29,858,000	$ 160,544,000	$ 69,522,000
Stock repurchased | shares				31,281,000		105,594,000
Stock repurchased, value				$ 332,891,000	55,870,000	$ 1,148,122,000	161,537,000
Portfolio company incentive compensation awards			$ 8,000,000
Amortization period of grant			4 years
Unrecognized compensation cost relating to portfolio company incentive compensation awards				3,800,000		$ 3,800,000
Unrecognized compensation cost recognition period						2 years 3 months 18 days
Recognized liabilities for Performance Participation expense				0	$ 56,322,000	$ 0	$ 106,383,000
Aggregate redeemable non- controlling interest shares and Class I units continue to own				225,900,000		225,900,000
Amount contributed to captive towards insurance premium				28,400,000		28,400,000
Payment for management fee				$ 500,000		$ 500,000
Class I Shares [Member]
Related Party Transaction [Line Items]
Stock repurchased | shares				22,552,000		57,120,000
Amortization 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						$ 18,900,000		42,100,000
Special Limited Partner [Member]
Related Party Transaction [Line Items]
Percentage of annual hurdle amount						5.00%
Related party allocation percentage of annual total return						12.50%
Special Limited Partner [Member] | Class I Shares [Member]
Related Party Transaction [Line Items]
Stock issued as payment for services | shares		11,700,000
Stock redeemed, shares | shares		7,300,000
Stock redeemed, value		$ 83,600,000
Stock exchanged, shares | shares		800,000
Special Limited Partner [Member] | Class B Shares [Member]
Related Party Transaction [Line Items]
Stock issued as payment for services | shares		700,000
Stock redeemed, shares | shares		7,300,000
All Other Unit Holders [Member]
Related Party Transaction [Line Items]
Related party allocation percentage of annual total return						87.50%
LivCor L.L.C. [Member] | Other Assets [Member]
Related Party Transaction [Line Items]
Receivable from affiliates				$ 3,900,000		$ 3,900,000		3,600,000
LNLS [Member]
Related Party Transaction [Line Items]
Costs paid to LNLS for title services related to investments						$ 2,600,000
Number of Investments with Capitalized or Deferred Financing Costs | Investment						20
Accrued Stockholder Servicing Fee [Member]
Related Party Transaction [Line Items]
Total components due to affiliates				572,784,000		$ 572,784,000		478,539,000
Advanced Organization and Offering Costs [Member]
Related Party Transaction [Line Items]
Total components due to affiliates				4,602,000		4,602,000		6,136,000
Advanced Expenses [Member]
Related Party Transaction [Line Items]
Total components due to affiliates				2,200,000		2,200,000		2,000,000
Accrued Management Fee [Member]
Related Party Transaction [Line Items]
Total components due to affiliates				19,869,000		19,869,000		13,873,000
Accrued Management Fee [Member] | Adviser [Member]
Related Party Transaction [Line Items]
Total components due to affiliates				$ 19,900,000		$ 19,900,000		$ 13,900,000
Management Fee [Member] | Adviser [Member] | Class I Shares [Member]
Related Party Transaction [Line Items]
Stock issued as payment for services | shares						13,006,077	5,288,447
Stock repurchased | shares						8,418,835	6,614,229
Stock repurchased, value						$ 89,500,000	$ 72,700,000
Management Fee [Member] | Subsequent Event [Member] | Adviser [Member] | Class I Shares [Member]
Related Party Transaction [Line Items]
Stock issued as payment for services | shares	1,778,962