Common Stock and Other Equity Related Transactions - Additional Information (Detail) - $ / shares	3 Months Ended
	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015
Class of Stock [Line Items]
Preferred stock dividends paid (usd per share)	$ 0.421875	$ 0.421875	$ 0.421875
Common Stock dividends paid (usd per share)	$ 0.375	$ 0.375	$ 0.375
6.75% Series C Cumulative Redeemable Perpetual Preferred Stock
Class of Stock [Line Items]
Date to be paid	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015
Date of record	Sep. 18, 2015	Jun. 19, 2015	Mar. 20, 2015
Common Stock
Class of Stock [Line Items]
Date to be paid	Oct. 09, 2015	Jul. 10, 2015	Apr. 10, 2015
Date of record	Sep. 25, 2015	Jun. 26, 2015	Mar. 27, 2015