Stockholders' Equity - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands			1 Months Ended			3 Months Ended					9 Months Ended
	Jun. 30, 2020	May 09, 2020	Jun. 30, 2021	May 31, 2021	Feb. 28, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020	Jun. 16, 2021
Class of Stock [Line Items]
Issuance and redemption costs of redeemed preferred stock						$ 0			$ 0		$ 4,682	$ 0
Number of shares repurchased during period (in shares)						0			0		0	0
Common stock dividend percentage of cash limit		10.00%
Common stock dividends		$ 8,200				$ 28,057	$ 26,071	$ 22,176	$ 9,070	$ 82,483
Common stock dividends (in shares)	16,338,511
Payments of ordinary dividends, common stock	$ 8,200
Common stock dividends shares calculation base (in USD per share)	$ 4.5435
Restricted Stock
Class of Stock [Line Items]
Shares granted during the period (in shares)				127,115
Preferred Stock
Class of Stock [Line Items]
Preferred stock, redemption price per share (in USD per share)						$ 25.00					$ 25.00
Equity distribution agreement, authorized (in shares)											5,500,000
Series A Preferred Stock
Class of Stock [Line Items]
Preferred stock, redemption amount													$ 140,000
Preferred stock, liquidation preference (in USD per share)													$ 25.00
Preferred stock dividend rate											7.75%
Preferred stock, dividends per annum (in USD per share)											$ 1.9375
Series B Preferred Stock
Class of Stock [Line Items]
Preferred stock, liquidation preference (in USD per share)						$ 25.00					$ 25.00
Preferred stock dividend rate											7.75%
Preferred stock, dividends per annum (in USD per share)											$ 1.9375
Series B Preferred Stock | LIBOR
Class of Stock [Line Items]
Preferred stock dividend variable rate spread						5.18%					5.18%
Series C Preferred Stock
Class of Stock [Line Items]
Preferred stock, liquidation preference (in USD per share)						$ 25.00					$ 25.00
Preferred stock dividend rate											7.50%
Preferred stock, dividends per annum (in USD per share)											$ 1.875
Series C Preferred Stock | LIBOR
Class of Stock [Line Items]
Preferred stock dividend variable rate spread						5.289%					5.289%
Common Stock
Class of Stock [Line Items]
Number of shares issued during period			43,125,000		27,600,000
Sale of stock, price (in USD per share)			$ 3.39		$ 3.75		$ 3.39
Proceeds from issuance of common stock			$ 145,900		$ 103,100
Remaining number of shares authorized to be repurchased (in shares)						18,163,982					18,163,982
Common Stock | Equity Distribution Agreement
Class of Stock [Line Items]
Number of shares issued during period						22,060,000			25,431		37,610,000	25,431
Proceeds from issuance of common stock						$ 67,500			$ 80		$ 125,400	$ 80
Payments of stock issuance commission and fees						$ 1,000			$ 2		$ 1,800	$ 2