Common and Preferred Stock (Detail) - USD ($)			12 Months Ended
	Aug. 03, 2017	Jun. 19, 2015	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jun. 30, 2025	Sep. 30, 2022	Dec. 31, 2007
Common Stock [Line Items]
Net proceeds from issuance of common stock			$ 2,957,000	$ 2,704,000	$ 8,207,000
Repurchase Plan
Common Stock [Line Items]
Amount authorized under share repurchase program								$ 4,700,000
Number of shares repurchased (in shares)			0	0	0
Other Stock Repurchases
Common Stock [Line Items]
Number of shares repurchased (in shares)			175,000	441,000	218,000
Average price of shares purchased (in usd per share)			$ 10.45	$ 11.83	$ 12.12
Dividend Reinvestment Plan
Common Stock [Line Items]
Number of shares reissued from treasury stock (in shares)				87,000	713,000
Proceeds from treasury stock reissued				$ 1,000,000.0	$ 8,200,000
Series A Preferred Stock
Common Stock [Line Items]
Stock issued (in shares)		4,600,000
Liquidation preference per share (in usd per share)		$ 25
Fixed dividend rate per annum		6.25%
Proceeds from issuance of preferred stock, net of issuance costs		$ 111,600,000
Series A Preferred Stock | LIBOR | Forecast
Common Stock [Line Items]
Spread on variable dividend rate per annum						3.85%
Series B Preferred Stock
Common Stock [Line Items]
Stock issued (in shares)	4,000,000.0
Liquidation preference per share (in usd per share)	$ 25
Fixed dividend rate per annum	5.50%
Proceeds from issuance of preferred stock, net of issuance costs	$ 98,100,000
Series B Preferred Stock | LIBOR | Forecast
Common Stock [Line Items]
Spread on variable dividend rate per annum							3.578%