Series B Cumulative Convertible Preferred Stock - Additional Information (Detail)	3 Months Ended	9 Months Ended
	Sep. 30, 2019 item director $ / shares shares	Sep. 30, 2019 item director $ / shares shares	Dec. 31, 2018 $ / shares
Conversion Of Stock [Line Items]
Series B Cumulative Convertible Preferred Stock, par value | $ / shares	$ 0.01	$ 0.01	$ 0.01
Series B Cumulative Convertible Preferred Stock, liquidating preference per share | $ / shares	$ 25.00	$ 25.00	$ 25.00
Series B Preferred Stock
Conversion Of Stock [Line Items]
Preferred Stock, dividend rate		6.25%
Preferred Stock, conversion start date		Jan. 25, 2012
Number of transactions to convert preferred stock	0
Conversion of preferred stock, conversion rate (in shares) | shares	5.4397	5.4397
Number of consecutive trading days used in conversion analysis		30
Minimum number of quarters with failure to pay dividends, which triggers voting rights for preferred stock, quarters	6	6
Number of Board Of Directors that Preferred Stock owners are entitled to vote to elect when there is a failure to pay quarterly dividends for a set period | director	2	2
Minimum ratio of votes required to materially and adversely change the terms of preferred stock	66.67%	66.67%
Series B Preferred Stock | Minimum
Conversion Of Stock [Line Items]
Percentage of common stock price to then-prevailing conversion price in order to exercise conversion option		130.00%
Number of consecutive trading days used in conversion analysis		20
Series A Preferred Stock
Conversion Of Stock [Line Items]
Preferred Stock, dividend rate		8.625%
Series C Preferred Stock
Conversion Of Stock [Line Items]
Preferred Stock, dividend rate		7.625%