Organization and Summary of Significant Accounting Policies (Schedule of Distributions Paid to Shareholders) (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Component Of Operating Cost And Expense [Line Items]
Ordinary income	$ 0.25	$ 0.00	$ 0.00
Non-dividend distributions	0.59	0.84	0.84
Distribution paid to shareholders	0.84	0.84	0.84
Series A Preferred Shares[Member]
Component Of Operating Cost And Expense [Line Items]
Non-dividend distributions		1.70	2.06
Distribution paid to shareholders		1.70	2.06
Series B Preferred Shares [Member]
Component Of Operating Cost And Expense [Line Items]
Ordinary income	1.84	0.00
Non-dividend distributions	0.00	1.84	1.84
Distribution paid to shareholders	1.84	1.84	$ 1.84
Series C Preferred Stock [Member]
Component Of Operating Cost And Expense [Line Items]
Ordinary income	1.80
Non-dividend distributions	0.00	1.59
Distribution paid to shareholders	1.80	1.59
Series D Preferred Stock [Member]
Component Of Operating Cost And Expense [Line Items]
Ordinary income	1.72	0.00
Non-dividend distributions	0.00	0.45
Distribution paid to shareholders	$ 1.72	$ 0.45