Equity Offerings (Narrative) (Detail) (USD $)	1 Months Ended			12 Months Ended			1 Months Ended			1 Months Ended		1 Months Ended
	May 31, 2013	Oct. 31, 2012	Apr. 30, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Oct. 31, 2012 Term Loan [Member]	Apr. 30, 2012 Series A Preferred Shares, $.01 par [Member]	Oct. 31, 2012 Series A Preferred Shares, $.01 par [Member]	Oct. 31, 2012 Series B Preferred Shares, $.01 par [Member]	Apr. 30, 2012 Series B Preferred Shares, $.01 par [Member]	Dec. 31, 2012 Series A And Series B Preferred Shares [Member]
Class of Stock [Line Items]
Common stock shares issued	11,500,000			68,293,000	56,331,000
Common stock issuance price per share	$ 20.00
Net proceeds from shares issued in public common offering	$ 220,500,000			$ 220,511,000	$ 0	$ 0
Payment of under writing discounts and commissions	$ 0.80
Amount outstanding	192,500,000
Cumulative redeemable perpetual preferred shares issued								4,600,000		3,450,000
Cumulative redeemable perpetual preferred shares, dividend rate								8.25%		7.375%
Public offering				$ 18.98					$ 25.00		$ 25.00
Payment of the underwriting discount								3,600,000		2,700,000
Payment of the underwriting discount per preferred share								$ 0.7875		$ 0.7875
Offering expenses								500,000		300,000
Net proceeds from the offering outstanding		15,000,000					58,000,000	30,000,000
Net proceeds from the offering received			110,896,000	220,511,000
Net proceeds from issuance of preferred shares										83,300,000
Redemption of Preferred Shares				$ 25.00
Redemption period, change of control				120 days
Accumulated but unpaid dividends relating to Preferred Shares												$ 700,000