Tax Characterization of Dividends per Share on Common Shares (Detail) - $ / shares		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019
Dividends Payable [Line Items]
Total Per Share		$ 0.44	$ 1.76
Dividend Payment 1st
Dividends Payable [Line Items]
Declaration Date		Feb. 21, 2019
Record Date		Apr. 01, 2019
Payable Date		Apr. 15, 2019
Ordinary Income	[1]	$ 0.383646
Return of Capital		0.056354
Total Per Share		$ 0.44
Dividend Payment 2nd
Dividends Payable [Line Items]
Declaration Date		May 16, 2019
Record Date		Jul. 01, 2019
Payable Date		Jul. 16, 2019
Ordinary Income	[1]	$ 0.383646
Return of Capital		0.056354
Total Per Share		$ 0.44
Dividend Payment 3rd
Dividends Payable [Line Items]
Declaration Date		Aug. 15, 2019
Record Date		Oct. 01, 2019
Payable Date		Oct. 15, 2019
Ordinary Income	[1]	$ 0.383646
Return of Capital		0.056354
Total Per Share		$ 0.44
Dividend Payment 4th
Dividends Payable [Line Items]
Declaration Date		Dec. 12, 2019
Record Date		Jan. 06, 2020
Payable Date		Jan. 15, 2020
Ordinary Income	[2]	$ 0.440000
Total Per Share		$ 0.44
Dividend Payment 5th
Dividends Payable [Line Items]
Declaration Date		Feb. 20, 2020
Record Date		Apr. 01, 2020
Payable Date		Apr. 15, 2020
Ordinary Income	[2]	$ 0.440000
Total Per Share		$ 0.44

[1] $0.042774 of this amount constitutes a "Qualified Dividend", as defined by the IRS.

[2] $0.040745 of this amount constitutes a "Qualified Dividend", as defined by the IRS.