Stock Transactions and Unit Redemptions - Additional Information (Details)	3 Months Ended				12 Months Ended
	Dec. 31, 2020 USD ($) vote class $ / shares shares	Sep. 30, 2020 $ / shares shares	Jun. 30, 2020 $ / shares shares	Mar. 31, 2020 $ / shares shares	Dec. 31, 2020 USD ($) vote shares class $ / shares	Dec. 31, 2019 USD ($) $ / shares shares	Dec. 31, 2018 shares	Aug. 01, 2018 USD ($)	Dec. 31, 2017 shares
Class of Stock
Number of authorized classes of common stock | class	2				2
Common Class A
Class of Stock
Common stock, votes per share | vote	1				1
Common stock, shares authorized (in shares)	1,000,000,000.0				1,000,000,000.0	1,000,000,000
Common stock, par value (in usd per share) | $ / shares	$ 0.01				$ 0.01	$ 0.01
Common stock, shares outstanding (in shares)	161,175,894				161,175,894	156,265,461	156,916,336		138,593,787
Treasury stock repurchases (in shares)	930,226	0	0	0	930,226	4,518,002	50,000
Shares repurchased price (in dollars per share) | $ / shares	$ 7.33	$ 0	$ 0	$ 0	$ 8.99	$ 9.32
Share repurchase and redemption unit remaining authorized amount | $	$ 150,596,000				$ 150,596,000	$ 157,413,000
Common Class A | Maximum | Limited Partnership Interests or Other Equity Interests in Subsidiaries | Affiliated Persons or Entities
Class of Stock
Stock repurchases and redeemed or repurchases authorized amount | $								$ 200,000,000
Common Class B
Class of Stock
Common stock, votes per share | vote	10				10
Common stock, shares authorized (in shares)	500,000,000				500,000,000	500,000,000
Common stock, par value (in usd per share) | $ / shares	$ 0.01				$ 0.01	$ 0.01
Conversion of common stock (in shares)					1
Common stock, shares outstanding (in shares)	21,285,533				21,285,533	21,285,533