Stockholders' Equity - Schedule of Preferred Stock Issued and Outstanding (Details) - USD ($)	1 Months Ended	9 Months Ended		12 Months Ended
	Jul. 30, 2021	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Class of Stock [Line Items]
Preferred stock, shares authorized (in shares)				30,900,000
Preferred stock, carrying value		$ 542,232,000		$ 504,765,000
Series B Preferred Stock
Class of Stock [Line Items]
Preferred stock, shares authorized (in shares)		6,000,000		6,000,000
Preferred stock, shares issued (in shares)		3,156,087		3,156,087
Preferred stock, carrying value		$ 76,180,000		$ 76,180,000
Preferred stock, liquidation preference		$ 78,902,000		$ 78,902,000
Preferred stock, contractual rate, percentage		7.75%		7.75%
Series C Preferred Stock
Class of Stock [Line Items]
Preferred stock, shares authorized (in shares)				6,600,000
Preferred stock, shares issued (in shares)				4,181,807
Preferred stock, carrying value				$ 101,102,000
Preferred stock, liquidation preference				$ 104,545,000
Preferred stock, contractual rate, percentage		7.875%		7.875%
Preferred stock, liquidation preference per share (in dollars per share)		$ 25.00
Series D Preferred Stock
Class of Stock [Line Items]
Preferred stock, shares authorized (in shares)		8,400,000		8,400,000
Preferred stock, shares issued (in shares)		6,123,495		6,123,495
Preferred stock, carrying value		$ 148,134,000		$ 148,134,000
Preferred stock, liquidation preference		$ 153,087,000		$ 153,087,000
Preferred stock, contractual rate, percentage		8.00%		8.00%
Series D Preferred Stock | LIBOR
Class of Stock [Line Items]
Preferred stock, floating annual rate, percentage		0.00057%	0.00057%
Series E Preferred Stock
Class of Stock [Line Items]
Preferred stock, shares authorized (in shares)	2,000,000	9,900,000		9,900,000
Preferred stock, shares issued (in shares)		7,411,499		7,411,499
Preferred stock, carrying value		$ 179,349,000		$ 179,349,000
Preferred stock, liquidation preference		$ 185,288,000		$ 185,288,000
Preferred stock, contractual rate, percentage		7.875%		7.875%
Series E Preferred Stock | LIBOR
Class of Stock [Line Items]
Preferred stock, floating annual rate, percentage		0.06429%	0.06429%
Series F Preferred Stock
Class of Stock [Line Items]
Preferred stock, shares authorized (in shares)	5,750,000	7,750,000
Preferred stock, shares issued (in shares)		5,750,000
Preferred stock, carrying value		$ 138,569,000
Preferred stock, liquidation preference		$ 143,750,000
Preferred stock, contractual rate, percentage	6.875%	6.875%
Series F Preferred Stock | Underwritten Public Offering
Class of Stock [Line Items]
Preferred stock, liquidation preference per share (in dollars per share)		$ 25
Series F Preferred Stock | LIBOR
Class of Stock [Line Items]
Preferred stock, floating annual rate, percentage		0.0613%
Preferred Stock, Series Shares
Class of Stock [Line Items]
Preferred stock, shares authorized (in shares)		32,050,000		30,900,000
Preferred stock, shares issued (in shares)		22,441,081		20,872,888
Preferred stock, carrying value		$ 542,232,000		$ 504,765,000
Preferred stock, liquidation preference		$ 561,027,000		$ 521,822,000