Earnings per Common Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Numerator:
Net income attributable to common shareholders	$ 21,758	$ 25,298
Less: Dividends paid on unvested restricted shares	(282)	(413)
Net income attributable to common shareholders excluding amounts attributable to unvested restricted shares	$ 21,476	$ 24,885
Denominator:
Weighted-average number of common shares - basic (in shares)	123,734,173	123,739,823
Unvested restricted shares (in shares)	107,227	402,001
Weighted-average number of common shares - diluted (in shares)	123,841,400	124,141,824
Net income per share attributable to common shareholders - basic (in dollars per share)	$ 0.17	$ 0.20
Net income per share attributable to common shareholders - diluted (in dollars per share)	$ 0.17	$ 0.20