Earnings per Common Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Numerator:
Net income attributable to common shareholders before discontinued operations (in shares)	$ 33,290	$ 15,917	$ 80,089	$ 28,568
Income (loss) from discontinued operations	3,179	(721)	5,387	(1,000)
Less: Dividends paid on unvested restricted shares (in shares)	(216)	(183)	(712)	(594)
Net income attributable to common shareholders	36,469	15,196	85,476	27,568
Less: Undistributed earnings attributable to unvested restricted shares (in shares)	(97)	0	(86)	0
Net income attributable to common shareholders excluding amounts attributable to unvested restricted shares (in shares)	$ 36,156	$ 15,013	$ 84,678	$ 26,974
Denominator:
Weighted-average number of common shares - basic (in shares)	121,594,219	105,453,978	116,697,417	105,392,071
Unvested restricted shares (in shares)	249,029	55,126	212,672	54,140
Unvested performance units (in shares)	906,873	0	887,581	0
Weighted-average number of common shares - diluted (in shares)	122,750,121	105,509,104	117,797,670	105,446,211
Basic per common share data:
Net income per share attributable to common shareholders before discontinued operations (in dollars per share)	$ 0.27	$ 0.15	$ 0.68	$ 0.27
Discontinued operations (in dollars per share)	$ 0.03	$ (0.01)	$ 0.05	$ (0.01)
Net income per share attributable to common shareholders (in dollars per share)	$ 0.30	$ 0.14	$ 0.73	$ 0.26
Diluted per common share data:
Net income per share attributable to common shareholders before discontinued operations (in dollars per share)	$ 0.27	$ 0.15	$ 0.67	$ 0.27
Discontinued operations (in dollars per share)	$ 0.03	$ (0.01)	$ 0.05	$ (0.01)
Net income per share attributable to common shareholders (in dollars per share)	$ 0.30	$ 0.14	$ 0.72	$ 0.26