Earnings per Common Share (Details) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Earnings Per Share [Abstract]
Undistributed Earnings Allocated to Participating Securities	$ 27,000
Numerator:
Net income attributable to common shareholders	47,850,000	11,932,000
Less: Dividends paid on unvested restricted shares	(279,000)	(246,000)
Undistributed Earnings, Basic	27,000	0
Net income attributable to common shareholders excluding amounts attributable to unvested restricted shares	$ 47,544,000	$ 11,686,000
Denominator:
Weighted-average number of common shares - basic (in shares)	131,272,611	121,740,962
Unvested restricted shares (in shares)	281,980	281,721
Unvested performance units (in shares)	731,951	845,072
Weighted-average number of common shares - diluted (in shares)	132,286,542	122,867,755
Basic per common share data:
Net income per share attributable to common shareholders (in dollars per share)	$ 0.36	$ 0.10
Diluted per common share data:
Net income per share attributable to common shareholders (in dollars per share)	$ 0.36	$ 0.10