Tax Information Regarding Dividend Distributions (Detail)	12 Months Ended
	Dec. 31, 2019 $ / shares
Common Stock
Dividends [Line Items]
Total Distribution Per Share	$ 0.560000
Ordinary Income	0.330884
Return of Capital	0.139116
Carry-Over to 2018	$ 0.090000
Declaration Date 12/14/18 | Common Stock
Dividends [Line Items]
Declaration Date	Dec. 14, 2018
Record Date	Dec. 31, 2018
Payable Date	Jan. 29, 2019
Total Distribution Per Share	$ 0.130000
Ordinary Income	0.091521
Return of Capital	$ 0.038479
Declaration Date 03/14/19 | Common Stock
Dividends [Line Items]
Declaration Date	Mar. 14, 2019
Record Date	Mar. 29, 2019
Payable Date	Apr. 29, 2019
Total Distribution Per Share	$ 0.130000
Ordinary Income	0.091521
Return of Capital	$ 0.038479
Declaration Date 06/13/19 | Common Stock
Dividends [Line Items]
Declaration Date	Jun. 13, 2019
Record Date	Jun. 28, 2019
Payable Date	Jul. 29, 2019
Total Distribution Per Share	$ 0.110000
Ordinary Income	0.077441
Return of Capital	$ 0.032559
Declaration Date 09/17/19 | Common Stock
Dividends [Line Items]
Declaration Date	Sep. 17, 2019
Record Date	Sep. 30, 2019
Payable Date	Oct. 29, 2019
Total Distribution Per Share	$ 0.100000
Ordinary Income	0.070401
Return of Capital	$ 0.029599
Declaration Date 12/17/19 | Common Stock
Dividends [Line Items]
Declaration Date	Dec. 17, 2019
Record Date	Dec. 31, 2019
Payable Date	Jan. 29, 2020
Total Distribution Per Share	$ 0.090000
Carry-Over to 2018	0.090000
8.625% Series A Cumulative Preferred Stock
Dividends [Line Items]
Total Distribution Per Share	2.695315
Ordinary Income	2.156252
Carry-Over to 2018	$ 0.539063
8.625% Series A Cumulative Preferred Stock | Declaration Date 11/06/18
Dividends [Line Items]
Declaration Date	Nov. 06, 2018
Record Date	Dec. 31, 2018
Payable Date	Jan. 15, 2019
Total Distribution Per Share	$ 0.539063
Ordinary Income	$ 0.539063
8.625% Series A Cumulative Preferred Stock | Declaration Date 02/28/19
Dividends [Line Items]
Declaration Date	Feb. 28, 2019
Record Date	Mar. 29, 2019
Payable Date	Apr. 15, 2019
Total Distribution Per Share	$ 0.539063
Ordinary Income	$ 0.539063
8.625% Series A Cumulative Preferred Stock | Declaration Date 05/07/19
Dividends [Line Items]
Declaration Date	May 07, 2019
Record Date	Jun. 28, 2019
Payable Date	Jul. 15, 2019
Total Distribution Per Share	$ 0.539063
Ordinary Income	$ 0.539063
8.625% Series A Cumulative Preferred Stock | Declaration Date 08/06/19
Dividends [Line Items]
Declaration Date	Aug. 06, 2019
Record Date	Sep. 30, 2019
Payable Date	Oct. 15, 2019
Total Distribution Per Share	$ 0.539063
Ordinary Income	$ 0.539063
8.625% Series A Cumulative Preferred Stock | Declaration Date 11/06/19
Dividends [Line Items]
Declaration Date	Nov. 06, 2019
Record Date	Dec. 31, 2019
Payable Date	Jan. 15, 2020
Total Distribution Per Share	$ 0.539063
Carry-Over to 2018	0.539063
6.25% Series B Cumulative Convertible Preferred Stock
Dividends [Line Items]
Total Distribution Per Share	1.971607
Ordinary Income	1.580982
Carry-Over to 2018	$ 0.390625
6.25% Series B Cumulative Convertible Preferred Stock | Declaration Date 11/06/18
Dividends [Line Items]
Declaration Date	Nov. 06, 2018
Record Date	Dec. 31, 2018
Payable Date	Jan. 15, 2019
Total Distribution Per Share	$ 0.395857
Ordinary Income	$ 0.395857
6.25% Series B Cumulative Convertible Preferred Stock | Declaration Date 02/28/19
Dividends [Line Items]
Declaration Date	Feb. 28, 2019
Record Date	Mar. 29, 2019
Payable Date	Apr. 15, 2019
Total Distribution Per Share	$ 0.396315
Ordinary Income	$ 0.396315
6.25% Series B Cumulative Convertible Preferred Stock | Declaration Date 05/07/19
Dividends [Line Items]
Declaration Date	May 07, 2019
Record Date	Jun. 28, 2019
Payable Date	Jul. 15, 2019
Total Distribution Per Share	$ 0.394509
Ordinary Income	$ 0.394509
6.25% Series B Cumulative Convertible Preferred Stock | Declaration Date 08/06/19
Dividends [Line Items]
Declaration Date	Aug. 06, 2019
Record Date	Sep. 30, 2019
Payable Date	Oct. 15, 2019
Total Distribution Per Share	$ 0.394301
Ordinary Income	$ 0.394301
6.25% Series B Cumulative Convertible Preferred Stock | Declaration Date 11/06/19
Dividends [Line Items]
Declaration Date	Nov. 06, 2019
Record Date	Dec. 31, 2019
Payable Date	Jan. 15, 2020
Total Distribution Per Share	$ 0.390625
Carry-Over to 2018	0.390625
7.625% Series C Cumulative Redeemable Preferred Stock
Dividends [Line Items]
Total Distribution Per Share	2.382815
Ordinary Income	1.906252
Carry-Over to 2018	$ 0.476563
7.625% Series C Cumulative Redeemable Preferred Stock | Declaration Date 11/06/18
Dividends [Line Items]
Declaration Date	Nov. 06, 2018
Record Date	Dec. 31, 2018
Payable Date	Jan. 15, 2019
Total Distribution Per Share	$ 0.476563
Ordinary Income	$ 0.476563
7.625% Series C Cumulative Redeemable Preferred Stock | Declaration Date 02/28/19
Dividends [Line Items]
Declaration Date	Feb. 28, 2019
Record Date	Mar. 29, 2019
Payable Date	Apr. 15, 2019
Total Distribution Per Share	$ 0.476563
Ordinary Income	$ 0.476563
7.625% Series C Cumulative Redeemable Preferred Stock | Declaration Date 05/07/19
Dividends [Line Items]
Declaration Date	May 07, 2019
Record Date	Jun. 28, 2019
Payable Date	Jul. 15, 2019
Total Distribution Per Share	$ 0.476563
Ordinary Income	$ 0.476563
7.625% Series C Cumulative Redeemable Preferred Stock | Declaration Date 08/06/19
Dividends [Line Items]
Declaration Date	Aug. 06, 2019
Record Date	Sep. 30, 2019
Payable Date	Oct. 15, 2019
Total Distribution Per Share	$ 0.476563
Ordinary Income	$ 0.476563
7.625% Series C Cumulative Redeemable Preferred Stock | Declaration Date 11/06/19
Dividends [Line Items]
Declaration Date	Nov. 06, 2019
Record Date	Dec. 31, 2019
Payable Date	Jan. 15, 2020
Total Distribution Per Share	$ 0.476563
Carry-Over to 2018	$ 0.476563