Common Stock and Other Equity Related Transactions - Additional Information (Detail) (USD $)	3 Months Ended			3 Months Ended							3 Months Ended
	Sep. 14, 2012	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2012 8.034% Series A Cumulative Redeemable Perpetual Preferred Stock	Jun. 30, 2012 8.034% Series A Cumulative Redeemable Perpetual Preferred Stock	Mar. 31, 2012 8.034% Series A Cumulative Redeemable Perpetual Preferred Stock	Sep. 30, 2012 Common Stock	Jun. 30, 2012 Common Stock	Mar. 31, 2012 Common Stock	Sep. 14, 2012 Cumulative Series C Six Point Seven Five Percent Redeemable Perpetual Preferred Stock [Member]	Dec. 31, 2012 Subsequent Event [Member]	Dec. 31, 2012 Subsequent Event [Member] 8.034% Series A Cumulative Redeemable Perpetual Preferred Stock	Oct. 18, 2012 Subsequent Event [Member] 8.034% Series A Cumulative Redeemable Perpetual Preferred Stock
Class of Stock [Line Items]
Dividends Payable, Date to be Paid				Sep. 28, 2012	Jun. 29, 2012	Mar. 30, 2012	Oct. 12, 2012	Jul. 13, 2012	Apr. 13, 2012
Common Stock, Dividends, Per Share, Cash Paid							$ 0.4375	$ 0.4375	$ 0.4375
Preferred Stock, Dividends, Per Share, Cash Paid				$ 0.502125	$ 0.502125	$ 0.502125
Dividends Payable, Date of Record				Sep. 17, 2012	Jun. 18, 2012	Mar. 19, 2012	Sep. 28, 2012	Jun. 29, 2012	Mar. 30, 2012
Preferred Stock, Shares Authorized		7,391,304	2,000,000	2,554,235						54,458
Preferred Stock, Liquidation Preference Per Share										$ 2,500.00			$ 25.00
Peferred Stock, Shares Exchanged	5,445,765
Depositary Shares, Issued	5,445,765
Depositary Share, Liquidation Preference Per Share	$ 25.00
Preferred Stock, Dividend Rate, Per-Dollar-Amount	$ 0.3849625										$ 0.0948460
Stock Redeemed or Called During Period, Shares												2,554,235
Stock Redeemed or Called During Period, Value												$ 64,100,000
Common Stock, Par or Stated Value Per Share		$ 0.01	$ 0.01
At The Market Offering Value		$ 125,000,000